That's very interesting but irrelevant. People aren't using the term as a reference to game theory, they're using it as a cowardly way to say "You don't actually believe what you're saying."

When people are using this term, they are often implying that the ones signalling are trying to send false information to others. By signaling virtue they will be treated like a virtuous person even when they are immoral. The implication is that people virtue signalling are conscious that they don't believe what they say, but still say it for the sake of gain.