It is the new, hip way of describing something that is totally cool and unique. Another variant could be "signacha".
That restaurant we went to today was SO signature dude!" or "My kid is like no other. She's signature yo!
From the latin "oscit" for yawn; the fear or act of being extremely annoyed by people yawning; the sound, look or even thought of of people yawning. Especially applies to the "fat person yawn" where the flabby jowls jiggle and the mouth is gaping open while the person exhales a large nauseating and warm breath. Also, oscitophobe: someone who suffers from this phobia.
Tom, *yawwwwwn*. Julia, "Oh my gawd! Would you stop yawning?! That is so freakin annoying!" Tom, "Stop being such an oscitophobe! It's normal to yawn. Take your oscitophobia elsewhere you non-human!"