There are inside jokes hidden on set.
Many of the tubes that could be seen on the ship’s set of the original Star Trek series had the inscription “GNDN,” which stood for “Goes nowhere, does nothing.” It was a little inside joke they had that was replicated on the ships made years later.
Of course, this hand gesture means "read between the lines"...
He came up with it for the character. He's the reason it's in the show. That's all that anyone needs to know. Pointy ears weren't a new thing, either.