The Dog's Working?

Conversation overheard while standing in line today at Subway.

Guy #1 to his dining companion: That dog's working.

Guy #2: Huh?

Guy #1: It says on his thing right there, please don't pet me, I'm working.

Guy #2: The dog's working?

Guy #1: That's what it says.
 
Guy #2: What's that mean?

Guy #1: I think it's one of those Seeing Eye Dogs.