I think a lot of work is being done by the phrase "have functional value" in your description. Wearing head covering keeps God happy, standing for the anthem keeps you from being harassed in the press. Is all signaling, or all group-membership-signaling silly? Ok, probably yes. And really, for group distinction, the sillier the better.
But this means that almost all online social behavior is silly. Huh, now that I write it, I see how valid the description is.