From Minaide, Hizukashii:

What’s the deal with those yaoi paddles, anyway? I saw three different kinds for sale (and they were expensive, too! Like $30 each!): ones that said “UKE”, ones that said “SEME”, and ones that said “HARDCORE SIDE” and “SOFTCORE SIDE”. Do you smack people because they are yaoi-ing it up? Do you smack them so they will yaoi it up?

The answer is, of course, "both".