>>33293062 (OP)Going on 4chan for advice on how to ask out strangers is hilarious.
My advice would be to just be really direct and be like
"Hi, I think you're really cute. Here's my number." or some shit and then wait for their reaction.
Giving her your number lets her think she's safe because she didn't have to give away her personal information to a stranger, and it gives her the agency of deciding when to call, and it also gives you a good indication of whether or not you're her type. If she rejects your number, she wants nothing to do with it. If she takes it, she's considering it but may or may not be so sure. If she calls you eventually, then you've got a chance. If not, move on.