Squirrel Underpants

I just got back from a little vacation in Los Angeles where I came across something quite odd (of course I found more than one odd thing about LA, but this one is semi-relevant). We were cruising around in our rental car along Pacific Coast Highway and while we were stopped in traffic, I looked over and saw this sign in a pet store window...

Please, can anyone tell me why squirrels need underpants? Are they common pets in California, because in Colorado, we only see them in the wild, while we are trying to keep them out of our trail mix?

I just got a kick out of the sign, especially the small words on the bottom..."Got Nuts?"