Maybe like an eye with a cross icon or something, it would appear next to their nameplate like the mute icon. This would let you know the person you're looking at doesn't see your avatar, either due to not finished loading, or they've turned off avatars. That way I don't look like an idiot trying to show off a gesture animation and all they see is a robot thing flailing it's arms. Or in the case of switching avatars, I'll know when I am safe to use my animations again so we don't desync.