I would put something that is non-obvious and hopefully marginally unique. This would likely mean nothing with a Dilbert, xkcd, or space theme.
My walls tend to have unique artwork, and/or framed versions of my own photographs. I like when my office wall art can inspire a conversation vs. a "heh heh, funny" sort of response.
My walls tend to have unique artwork, and/or framed versions of my own photographs. I like when my office wall art can inspire a conversation vs. a "heh heh, funny" sort of response.