It all boils down to campus versus city jurisdiction, but even though campus police CAN get you, they don't. Monroe Street Fair takes place off campus (unlike the diag/Hash Bash) and nobody needs a card there. It's like walking into a public park that is hosting a free outdoor concert. Actually, it IS a public outdoor free concert lol. There are some vendor booths set up there by the different clubs scattered around Michigan and I'm sure they will expect to see a card if you intend to cop anything, but other than that no, nobody ever asks for a card. Too many joints coming at you from all directions for anybody to give a shit.