Now that you have the history, here's an update. I think the Big Cowboy originally advertised a muffler shop and he held a big muffler in his hands.
But in later reincarnations, his hands were empty.
I drove by today and stopped to take a picture. Lo and behold, someone has a different idea. Take a look at what he has in his right hand.
Like any good gambler, he's holding the cards so I can't see what they are but from the smile on his face, I think Big Johnson has four aces!