what?

On friday I took my Father to get a tattoo, which came out really well. It's beautiful. But this isn't about the tattoo, it's about the loons that wander in and out of the shop all day. The shop is in an odd little part of town and there are always guys with varying degrees of sketchiness roaming around.

I'm sitting there chatting with Paul and then I notice some guy shuffling around.
His shirt read "WILL WORK FOR RABIES."

I don't have any idea what that means.