TabbedOut requires each user to use a five-character alphanumeric code, similar to the kind you'd get when booking an airline ticket. I'm not sure how the bartender is supposed to remember everyone's code (let alone people who have had too much to drink), but that's the general idea.
When I've used this in bars they have asked me to show them or tell them my code. It's already up on their POS system and has my name attached as well, so for future use I can just say my last name like I normally would even if they had my card.
Generally there are only a few people using TabbedOut at any given time, if not just me, so it's not hard for the bartender to remember me (bar tenders are quite good at remembering faces and names as they do it so often).