Civic Government (Scotland) Act 1982, section 14, wrote:
Signs on vehicles other than taxis.
(1) Subject to subsection (2) below, there shall not be displayed on or in a private hire car any word, sign, notice, mark, illumination or other feature which may suggest that the vehicle is available for hire as a taxi.
(2) Subsection (1) above does not apply in relation to any licence plate or other thing issued by the licensing authority for the purpose of indicating that the vehicle to which it relates is a private hire car or in relation to any sign required by virtue of section 21 of the Vehicles (Excise) Act 1971.
Saw an almost new PHV in the St Andrews area today (according to the MoT database it's only six weeks old) with the registration number
KY16 CAB 
(KY16 is the first part of the local postcode for Fife - KY being Kirkcaldy.)
If I was that way inclined I'd complain to the council, particularly when they failed an annual inspection on one HC because the number plate was 'illegal', and as far as I know that was simply because the tiny lettering with the supplier's name and address wasn't on the bottom of the number plate (which absolutely no-one except the most nitpicking vehicle inspector would ever notice).
But I'm not that way inclined, so it's just

from me, and I doubt if anyone else knows that particular rule. I mean, it seems no one at the council knew it when the vehicle was presented
