I wouldn't say I make weird faces.... But I find that my hands are usually "twirling the notes" in the air. That's a little odd. :)
Channeling Joe Cocker, are you? I don't think that's odd at all. Mick Jagger does it. Stevie Nicks does it, too. It's quite natural for hands to participate. Much more practical than, say, dancing.
For me, my hands are usually employed as headphone clamps so no invisible-orchestra conducting is possible. However, I'm most comfortable playing the piano or organ while singing, even if the keyboard isn't being recorded.