KXOK

St. Louis, Missouri's KXOK began broadcasting in 1938 at 1250 on the AM dial.  Two years later they moved down to 630 AM where they would remain for over five decades.  KXOK pioneered the Top-40 format in the early 1950s and at one point was one of the five most listened to stations in the country (along with another St. Louis station KMOX.)  From all accounts, KXOK was a beloved station for a certain generation of listener and has been described as St. Louis' American Graffiti.  Tribute sites can be found here, here and here. 
The above sticker probably dates to one of KXOK's post-1975 format changes which included Talk, Oldies and News.  630 AM is currently KYFI, part of BBN's network of Religious stations.