I need something that can help me tell if a house guest has communist brainworms, but doesn't signal anything to the uninfected. I was thinking something like a print of one of the Diego Rivera murals where Lenin is lurking in the background. I need some more ideas. It could be music, some choice phrases, some prominently displayed literature, etc. But it has to only be meaningful or interesting to the already initiated.

Edit: My wife is pretty sure that a normal American does not know what Lenin looks like. However, a portrait of Lenin won't work as a shiboleth if I'm asked to explain who he is.