This isn't a formal reward tier, because I wanted it to be available to everyone who showed up fast.
So the way to find this out is to check your backer number. If it's 17 or less, and your pledge is $10 or more, you're in! (Two of the first 15 were $1 pledges, so they don't count.)
I'll confirm those numbers when the campaign ends, and then in the post-campaign backer survey I'll ask you for details -- the prompt you want to be sketched, and the name you want to be credited by.