The 3rd Greek word is "Duocycloi", which is clearly "bicycle". My Greek vocab runs out there, though!

I always thought that was some (not so) secret Greek society headquarters. That could be that whenever I've passed that sign I've had a few pints in the Maypole and I'm musing conspiratorially.

You would expect the Greek to say the same as the Latin, but it goes (let me transliterate first): Enthade lefthentes duokukloi diaftharesontai. Literally something like: "Here caught bicycles will be destroyed." Which in English idiom might read: Bicycles found here will be destroyed. There may be an intended pun with the second word, as it sounds close to "left", thus making the thing a mock Greek sentence. But the idea of the "Destroyer" stands and is a good one... what can befall to bicycles in the Duchy of Cambridge! I love this sign too and I took a picture years ago for friends and students in Classics. Thanks for your excellent blog and resources. Lovely pictures for Cambridge lovers.