Since you're too much of a dumb SJW cuck to figure it out, let me spell it out for you.
The intent of someone who is virtuous, whatever that virtue may be, is to uphold that virtue itself. They take actions necessary to uphold those virtues; not for attention, or approval, but due to the literal Captain America "No, you move."
By contrast, "virtue signalers" don't actually have any virtues. These are the kind of people who will donate $1 to their church, and then spend the rest of the week blogging all over social media as to how they're supporting their church. Or, in the case of ANTIFA, spend all week trying to gain approval from one another about how they're going to "bash the fash" or some other useless shit. If they were the only one to show up to a protest, they would immediately leave, because they don't actually stand for anything.
It's almost synonymous with, but only a little broader than "Facebook Activism", aka, being a useless piece of shit for the entire sake of approval.