I think people are too hung up on this issue of “virtue signaling.” This phrase has become another right-wing bugaboo about PC culture run amok.
I’ll say it again: Trans and non-binary folks are asking cisgender folks (like me) to do this small thing to help them. There is no harm in it to me, so I do. That’s it. No big deal. There’s no “signalling” about how awesome I am. It’s just a simple courtesy.
If you’re having trouble with the idea, just imagine a good friend, who happens to be trans, asked you politely: “Hey friend, if you don’t mind, it would be great if you would put your pronouns in your email sig. It would help me and others like me out a little.” Then act accordingly.