It looks like a V, right? Ah, but it's not! If you look closely, you can see that the apparent V is actually a V and an I next to each other — the Roman numerals for 6. Colchester (as Camulodunum) was the capital of Roman Britain before Boudicca did that burn-it-to-the-ground thing, so Roman numerals make sense. Thus, although it looks like a V, really it's a VI! Clever stuff.
Except, why make it look like a V?