Above is a web page which shows a few early Sri Lanka plates on trolleybuses. The double-deckers use the code ‘CV’ which RPWO lists as ‘diesel buses & lorries’ – so perhaps CV also covered electrically-driven vehicles, too…..
I had once thought that it indicated ‘Conduit Vehicle’, as trams and trolleys rely on the overhead conduit for electric power, but no.
And while we’re in Ceylon:
In 1940, someone had he odd idea of creating a Sinhalese registration series which used the letters of the name of Ceylon as a component of the tag. Thus CE, CY, CL, CO(not issued ) and CN were succeeded by to EY, EL, and EN. The idea was then abandoned before YL began, and in 1956 the first ‘sri‘ symbol plates were launched.