Here is the original: http://www.johnbarrowman.com/fanzone/outabout/images/gavininterview/bbp.jpg
As you can see, it is very literally. Barrow-Man and Barker (the dog). Apparently it was made after a real dog Gavin once saw at a street but couldn't take with him.
And this is my take on it.
PS: You know you are famous when your ebay-seller and all the workers in their office wonder what you are gonna do next ;)