WLS

WLS 890 AM was originally owned by Sears, Roebuck and Company hence the call letter meaning of World's Largest Store.  They are one of the original 50,000-watt clear channel stations and went on the air in April, 1924.  WLS's standard bearing Top-40 era began in 1960 and lasted well into the mid-1980s when a transition to Adult Contemporary and Oldies began.  Talk shows then started appearing alongside music programming and by August, 1989 WLS dropped music altogether to go 24/7 Talk.
Some great WLS tribute and history sites can be found online.  Another semi-complete set of WLS stickers can be seen here.