5 for Vendetta ?
"V" can stand for many things, 5th of November?
shareGood catch.
shareOf all the people that were experimented on, only 5 survived initially and were isolated in cells. In the graphic novel, V claims to have lost his memory and bases his persona on the number of the cell he was held in - "V" or "5".
It's also in the movie (around 59:30 minutes in). (Rewatching that scene again, you can also see crosses on the prison cells, which V tells Creedy to mark his door later on to notify him if he agrees with his plan or not. Didn't notice that detail before.)