It's been puzzling me too, Emdee. I googled "Highlander Bar", and that seems to have been a fairly common pub name frequently used without the introductory "The" which would suit that particular theory. I ventured a guess at "Rest" because there must surely only be enough space left for a short-ish word, given the size of the lettering and the likely length of the building? But "Bar" seems much more likey. This is assuming it is a pub, I mean, what are the chances of a commercial building in Campbeltown being a pub?
Surely it must appear on some documentation somewhere, or is that just being naive?