Wikipedia's article on virtue signaling traces its history to its use by academics, but then notes
- Virtue signaling rose in popularity as a pejorative term, denouncing empty acts of public commitment to unexceptional good causes. In Bartholomew's original article, he describes virtue signaling as a public act with very little associated cost that is intended to inform others of one's socially acceptable alignment on an issue.
At some point, it appears, conservatives began to notice this term and its pejorative usage, and noted that it is primarily aimed at progressives/postmodernists or their acolytes. At this point it became obvious that the acolytes were obeying a kind of herd instinct, and it is frequently used by activist conservatives to point to the shallowness of the practitioners of virtue signaling.
As such, it has entered the domain of heated political discourse as a kind of tit-for-tat where, in particular, conservatives are accused of Dog Whistle politics.