The Amoco Sign actually originally was another brand name, but the cool Modernist gas station below it still serves the busy corner of Skinker and Clayton.
It’s one of two gas stations built in the middle of Clayton Road, the other being at Big Bend.
Several great links ti the original sign, which was HUGE (it was razed during my soph year at SLU)! The first shows how immense was it: http://theoldmotor.com/?p=129003
The second is from the current stations’ site: http://www.amocohipointeautoserviceandwash.com/index.cfm?pnav=3
I forgot – the current Amoco sign is the largest in the world! See http://www.atlasobscura.com/places/world-s-largest-amoco-sign