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On the watch when you select a contact the scatch icon will show center below picture or icon. This means you can sent a watch scatch
 
So is there a way to quickly go through my 500 contacts to see who has an Apple watch?
 
just to clarify you have to add a contact to your friend circle to see the hand.
I was about to say "what a bunch of hooey," but it looks like what you say is true.

I've got a coworker who has sent me a sketch or two just for fun (maybe he's trying to demonstrate it to his wife, for all I know), and it had the sketch/tap button available when it was time to reply. It's been weeks, though, and tonight, if I want to initiate a message, the tap/sketch option isn't there.

He's got me added to one of his circles of friends, but I haven't put him in mine.
 
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