Ranger has been seen at the dog park walking up to people with treats in their pockets, sitting politely and signing food. He certainly understands there is a sign he can make indicating he wants a treat. Fortunately for him he has me to interpret as most people have no idea that he is communicating with gestures. Most of his targets do recognize that he's begging. And most of them when I explain what he's doing respond by giving him treats.
I've begun teaching him the sign for cheese. I had a few Cheetos left in a bowl and he was hanging out and I'm too tired to exercise with him (remind me that I'm not 25 anymore and really do need to get my eight hours) so I took advantage of the circumstances. I haven't shaped his signs before but for cheese (left paw lift wrist bent) I'd push on the back of his wrist to get the proper bend. It didn't take long before he was understanding that to get the Cheeto he had to lift his paw and bend the wrist. He's a pretty smart dog.