Giant's Causeway, Portrush and Bush Valley Tramway
History
Although the tramway was promoted as an electrically operated venture, problems with commissioning the power plant meant that all services were initially operated by steam trams (from 1883); furthermore, as the electric trams were not approved for street running — due to the use of a side-contact conductor rail — the services within Portrush and Bushmills were intentionally built with steam operation in mind. Steam operations did not however cease following conversion to overhead electric pick-up in 1899, but instead continued up until the mid 1920s, mainly due to their much greater carrying capacity, often being used to replace electric services rather than simply supplementing them. The line finally closed in 1949.
Uniforms
Drivers working the steam services wore typical railway footplate-like attire, namely: waistcoats (probably self-purchased), light-coloured cotton jackets and the fashionable working-man's headgear of the day, principally the flat cap. No badges of any kind were carried. Conductors on the other hand wore waistcoats (possibly company issued), along with single-breasted uniform jackets (with lapels), and soft-topped caps; the jackets do not appear to have carried any badges, and surviving photographs are not of sufficient quality to discern whether the caps were similarly unadorned. Drivers working the electric services were issued with the same uniforms as conductors.
At some point, possibly in the late 1880s, the soft-topped caps were superseded by smarter, kepi-style caps; these new caps carried a lighter-coloured hat band, which bore Electric Tramway in embroidered script lettering. The kepis were eventually replaced by military-style caps with wide, tensioned crowns (tops), possibly around 1910, and it would seem likely that they continued to carry the same hat band. Many photographs from the 1920s onwards show staff in informal attire, whilst others clearly show crews wearing the standard military-style cap; a likely explanation for this is that the men without uniforms are relief crews (probably tramway fitters and electricians), who would have supplemented the normal crews during peak times.
Photographs of tramway inspectors have not come to light, and it may be that the tramway never employed them. Likewise, and unlike the vast majority of British mainland tramways, there is no evidence that the company employed the services of women during either the Great War or the Second World War.
Further reading
For a history of the line, see: 'Giant's Causeway, Portrush and Bush Valley Railway and Tramway Co Limited' by John McGuigan; Ulster Folk and Transport Museum (1983). For a more photograph-orientated publication, see: 'Irish Railways in Pictures No 4: The Giant's Causeway Tramway' by Michael Pollard; published by the Irish Railway Record Society - London Area (2000).
Images
Steam tram drivers and conductors
An excellent study of Steam Tram No 3 with conductor and driver — photo undated, but probably taken in the late 1880s or 1890s. The driver is in railway footplate-like attire with cotton jacket and flat cap, whilst the conductor has a single-breasted jacket, waistcoat and soft-topped cap. Photo courtesy of Jim Kilroy, tram archivist at the National Transport Museum (see link).
An evocative summer-time photo of Steam Tram No 3, 'Dunluce Castle' at Giant's Causeway — photo undated, but probably taken around the turn of the century. Photo courtesy of David Gladwin, with thanks to Trevor Preece.
A blow-up of the above photo showing the driver, who is absolutely filthy, listening intently to the man on the track; the driver is wearing a shirt, waistcoat and flat cap. 
Steam Tram No 1 or No 2, with Power Cars Nos 4 and 7 in Portrush — although undated, this must have been taken prior to the conversion to overhead electric pick-up in 1899. The driver is wearing a cotton jacket, whilst the conductor has a single-breasted jacket with a cap. Photo courtesy of the Tramways and Light Railway Society, with thanks to David Voice.
Steam Tram No 3 again, but a photo which is thought to have been taken on 15th July 1933, well after it had left the tramway, seen here working for a contractor near the River Bann. Photo courtesy of Jim Kilroy, tram archivist at the National Transport Museum (see link).
Motormen and conductors
Two conductors stand with a fully laden toastrack trailer at Giant's Causeway in third-rail days — photo undated, but probably taken not too long after it opened in 1887. Both conductors are wearing single-breasted jackets and kepi-style caps. Photo courtesy of the Tramways and Light Railway Society, with thanks to David Voice.
A shot taken by photographer Robert French at the terminus at Giant's Causeway, and very possibly on the same day as the previous shot. The motorman — at the controls of Tramcar No 9 - is wearing a waistcoat, single-breasted jacket and a kepi-style cap; the latter has a hat band, but does not appear to bear a badge, though this is difficult to say for certain. Original photo believed to be held in the National Library of Ireland.
Conductor William Jubilee Maxwell — photo undated, but probably taken in the early-Edwardian era (he was born in 1887 and worked for the tramway for 14 years, presumably from around 1900 to 1914, when he enlisted). He died in 1919 from TB, possibly as a result of being gassed. His obituary states that he had been a motorman and electrician, though in this photo, he is clearly carrying a conductor's cash bag. His hat band bears embroidered script-lettering: Electric Tramway. He was the son of William Robert Jubilee Trail Maxwell, who was the Tramway Operational & Maintenance Engineer for 57 years. The whereabouts of the original image is currently unclear; please do let me know if you can shed any light on this.
A rare depot staff shot, probably taken around 1910. The uniformed men in military-style caps are presumably conductors and motormen, whilst those in light-coloured cotton jackets are probably steam tram drivers, the remainder being more than likely fitters. William Jubilee Maxwell is believed to be the individual standing on the back row, far right. The whereabouts of the original image is currently unknown.
A blow-up of the above photo showing two of the uniformed staff. Both men are wearing single-breasted jackets and military-style caps; the latter bearing a light-coloured hat band. 
Tramcar No 10 and crew at Giants Causeway — photo undated, but probably taken in the mid-to-late Edwardian era. Source unknown.
Tramcar No 9 captured at perhaps the most photographed location on the tramway, Dunluce Castle — photo undated, but probably taken in the 1920s; both the driver and the conductor are wearing informal attire and the large flat caps that were particularly popular during this decade. Photo courtesy of the Tramways and Light Railway Society, with thanks to David Voice.
An unvestibuled No 23 stands at the terminus at Giant's Causeway — photo undated, but probably taken in the 1930s. Photo courtesy of the Tramways and Light Railway Society, with thanks to David Voice.
A blow-up of the above photo showing the conductor (seated left) and motorman, both of whom are wearing plain, single-breasted jackets and military-style caps. The jackets were probably informal, so they may have been a relief crew.
Tramcar No 9 in unrebuilt condition at Giant's Causeway — photo undated, but probably taken in the late 1930s. Photo courtesy of Jim Kilroy, tram archivist at the National Transport Museum (see link).
A blow-up of the above photo showing the motorman (on the platform) and a man who is probably a passenger. The motorman appears to be wearing an informal jacket without badges of any kind, along with the usual military-style cap.
Another blow-up of the preceding photo, this time showing the conductor, again in what would appear to be an informal jacket and a military-style cap; the latter appears to carry a light-coloured hat band.
A rare view of a motorman, taken from behind, between White Rocks and Dunluce - photo undated, but probably taken in the late 1940s. Photo courtesy of Jim Kilroy, tram archivist at the National Transport Museum (see link).