How about a sticker saying 'What do you think of it so far? Rubbish!' or 'I don't believe it!' that you could put on your enemy's posters and manifesto.
Got any more? I posted a list of catch-phrases here recently
http://www.livejournal.com/~communicator/191825.html
- so many of them are strangely appropriate. 'I have a cunning plan...'