How is it virtue signalling? That's when someone brags verbally about their position or perspective based on social expectations.

Based on your use of the word "destructive" I assume you're talking about radical animal activists like the ones who sabotage industrial meat factories, often secretly and anonymously for their own safety.

So, do you really think these really are people who are ineffectual and desiring social reaffirmation of their views? If anything, this group of individuals are exactly those I would call to mind as ones who are not afraid to make actual change in the world they want to see, whatever it takes. Forget if you agree with them or not. It seems absurd to call them ineffective virtue-signallers.