Do You Work Here?

The day was fine, but there were lots of weird customers everywhere. I got asked "Do you work here?" a half-dozen times. I came SO close to saying, "No. I like dressing like this and I wear the nametag because I like everyone to remember my name." Or simply, "No," and walking off. Instead, I paused for a LONG time before answering with raised eyebrows and a "Are you stupid?" expression on my face, "Yeeeeeeeeeeeeeessssssssssssssssssssssssssssssssss. Can I help you?"

I mean, how difficult is it? I'll be sweeping the floor or merchandising new products or STANDING BEHIND THE CASH COUNTER and people will still come up to me and ask if I work there. HELLO! Do YOU usually clean the store when you go shopping?? Do stores YOU shop at let non-employees stand anywhere near the cash??

Is "Do you work here?" the way they ask for help? If so, they should say, "Excuse me, can you help me, please?" Oh, but that contains two polite phrases that they're too good to use with me, their lowly slave. Or is "Do you work here?" their way of saying that I'm not working hard enough? Well, first of all it's really none of their business how hard I'm working, but secondly, most of the time I'm working myself to death doing a dozen things at once. Or if they're confused because occasionally vendors or other people are around that are connected TO the store but not employees OF the store, then they can ask, "Can you help me?" Then if they're asking a vendor that, the vendor can say, "No, but I can get you someone who can."

How do you respond when asked that question? Got any responses that make the point that the person asking the question is stupid but without being offensive enough to get in trouble for?