I always took virtue signalling, as an insult, to mean "Look at me, I'm doing/saying this good thing" which is all for attention and not just because it's a good thing to do or even worse when they are being hypocrites and not actually being good. E.g. Giving money to the homeless but filming it and putting it on Facebook. Preaching about climate change on a private jet world tour. Being offended on behalf of someone else when it isn't something that would be offensive or companies that change their twitter logo to a rainbow but their middle east account doesn't. Enhancing the person's/businesses image/reputation is the primary reason for doing it rather than the will to do good. David Beckham being an LGBT advocate and then accepting money from Qatar to be an ambassador is a great example.
It gets used as an insult though whenever anyone brings anything up even when they aren't just virtue signalling.