There is a guy who rides an older Silver Wing in our area and every day I see him, his buddy, a little Pomeranian, stands up solidly on the gas tank. The dog is not harnessed and he doesn't hold it. It stands up there all by itself. That turns heads! My wife flipped out the first time she saw it.
When I was in the Isle of Man this summer there was a tourist on what looked like a BMW R1200 with an aluminum box built into the back of it. Contentedly riding rear guard was a dog about the size of a Border Collie.
Marty