A bunch of graffiti I found in Left 4 dead 2:
'Bonsoir, mes amis.' - Good evening, My Friends.
'R.I.P *Someone*. What a long, strange journey its been.'
'Amour, pour toujours.' - Love for always (Ever probably. French grammar fail)
'NAPOLEON BABIN RAN OFF LIKE A COWARD'
'Diane - Took Abel and went to the sugar mill' - (Origin of witches in HR?)
But by far one of the best was the Midnight Riders memorial graffiti that turns into a flame war against them.