Most of the time, the accusation of “virtue signalling” includes an implicit connotation of “hypocrisy”. But then, why introduce a new and obscure term for something we have known about for millennia?
The answer is that hypocrisy is a specific accusation that can be backed up, or refuted, by evidence. For example, if a church leader who claims to be a Christian advocates locking up innocent children, the case is pretty clear-cut.
By contrast, “virtue signalling” is an insinuation rather than a factual claim. It doesn’t need to be backed up, and usually isn’t. If the person accused of virtue signalling on the basis of a symbolic action shows that they are in fact making costly efforts in support of their cause, these actions are just added to the charge sheet.
The charge of virtue signalling doesn’t rely on the actual inconsistencies of individuals. Rather it relies on in-group shared negative perceptions of out-groups (inner city latte sipping lefties and so on).
To restate the central point, accusations of virtue signalling aren’t meant to promote virtue: rather to argue against it. Those who use the accusation want to score points in favor of behavior they aren’t willing to defend openly.
By contrast, it’s worth remembering the observation of La Rouchefoucald that “hypocrisy is the tribute vice pays to virtue”.