"Please limit your time to an hour if you are just browsing the internet, during our peak hours of -----------
The "atmosphere" of the coffee shop is the atmosphere of mutual communication -- the customers listen too. There is no need for these weird "receipt" codes, or things like that. I'd simply go to Starbucks. I mean, I've refused to go to a coffee shop because they fired a barista I've known for a long time -- if they suddenly said -- "Hey, you're not welcome here, freeloader" -- without a polite explanation, as above -- then there would definitely be backlash.