I am LGBT and not in favor of it being pressured or de-facto compulsory. I would hope it was popular enough that people understood what it meant so that trans people can have more acceptance and understanding. I don't have it in my email signature, but if my company released a policy saying it was acceptable, I might add it. I would probably not add it without management permission since it is their choice how they want to present their brand to their clients. I think strongly pushing it on straight people is more likely to create a backlash and create a counter-movement.