They were pretty common around the St Louis area, That sign says regular but Clark only sold premium (Clark Super 100) 100 octane. Their slogan was We are the premium people. A good friend of mine worked at the local Clark station all through high school and later on he wound up buying the station he worked at. During high school everyone would always go up to the Clark station to see where the action was as Carl knew everyone and he would see everyone all night long as they would roll in and out of the station.