It's the finger sign from Star Trek. 'Live long and prosper.'
McGee would want someone to point out that it was referred to, by fans of Star Trek, as "the Vulcan salute." I don't know if the Vulcans themselves had a term for it, but I would suppose they did. The hand would be displayed this way as a greeting or as a good-bye. The first speaker, traditionally, would say "Peace and long life" to which the response is "live long and prosper."
(offered only for McGee's sense of getting the lore correct -- and a cheap excuse to repost a cute Tony photo -- and as a frightening reminder that I remember this without having seen Star Trek for a long, long time... )