I've always thought a nice big flag or banner thing would be one with just the silhouettes of all the things we've won. So, 7 (or, by the time it would happen,

FA cups, the European cup, the league cups, the trophies etc etc *
All that shit.
It basically says far more than any old trying to be clever shit referencing popular culture.
* i know someone else does this, but can't remember. It's a good idea, though