Hm... I have a couple different ideas:
#1 - "I shot the sheriff... he was, in fact, a zombie"
#2 - "The flu is a lie"
#3 - "Why so serious?" (then have a large creepy smile next to it and write "ha ha" everywhere else on the wall)
I can probably think of more, but that's all I got on short notice. I might also do one of those "Safe-Room Journal" ideas where I write what happened between each saferoom I visit. Could be a fun way to tell another story.