Almost everything seems to serve for signaling at least somewhat.

Even with my example, which I think seems to have an unusually dense combination of commonality of being asked, how fun or interesting it seems, and how impartial or non-partisan the answer would be, you could certainly still signal being pessimistic by saying no, or all futuristic or something by saying yes, or whatever.

I think the point would be less to find something that wouldn't serve for signaling at all, and more to come up with something that would be the least infected with the most mind-killing sort of signaling. Anything sufficiently interesting and common probably has at least some non-trivial signaling incentives.