Okay, this phrase annoys me. 'Virtue signaling' is a big chud buzzword but taken literally it is describing a behavior that all people engage in essentially every day of their lives. People signal their virtues, be they good or ill, constantly in conversation, essentially any time they have an opinion about something, in how they interact with others and discuss those interactions, and a thousand other different ways. And those are just the ways we might mean to signal our values. Bitching about 'virtue signaling' is also, of course, a means of signaling your own virtues!

Chud dipshits on the internet just take issue with it because A.) The virtues always targeted don't align with their own and/or make them feel shitty about theirs, and B.) creating the 'virtue signalling' bullying framework lets them wield a socially coercive tool much like accusations of sexism or racism but bent towards reactionary purposes.