Need help with my ~moves~

Alright ladies, advice time!!! So there's this bank teller that I interact with everytime I go through the drive through to deposit my check. Now, I'm a very emotionally charged/sensitive person, so I can tell when there's a bit of connection vs. just making polite small talk. I reallllly want to ask for his number, but my dilemma is HOW. 1. He's in a drive through window at a bank-I'd have to slide my number through the collection box thing, and 2. I've met/talked to him only a handful of times, so I don't want to cross any lines in case I'm reading this all wrong and he has a girlfriend or something. He's super cute and seems really nice/cool. I'm a very blunt person so I don't mind making a move. BUTHOWCANIBESLICK. give me your best advice my dears!