You probably never noticed that they do until now.

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It seems that whenever you switch on the radio for your morning commute all you hear is “Time to wake up with K98.3,” or “WBLS will be right back after this commercial break.” If you listen closely you’ll notice that they all have something in common; the vast majority of radio stations start with the letter ‘K’ or ‘W.’

All radio stations have a four-letter identification code. The hosts of the show typically come up with a more catchy station name than just the four letters, but you still hear it sprinkled in with their morning announcements and other advertisements. And the two letters that you consistently hear date all the way back to when people used to send telegrams. Try decoding these common acronyms that you probably never knew stood for something.

In 1912, several countries attended a conference to discuss international radiotelegraphs. One of the things that came out of that meeting was the assignment or specific letters to identify each country’s radio and television signals. The United States was given the letters W, K, N, and A.

The letters ‘N’ and ‘A’ were given to military stations, but ‘K’ and ‘W’ were assigned out for commercial use. Radio stations east of the Mississippi River had to start their stations with ‘W’, and stations west of the Mississippi with ‘K’. There is some discrepancy though since radio stations that already existed before this rule was put in place weren’t required to change their name.

The three letters after the ‘K’ or ‘W’ can mean a few different things. Sometimes they represent the networks that own the radio station—for example, WABC, KCBS, and WTBS. Sometimes it’s the actual station number, like in KTWO or KFOR. And other times it’s an acronym such as WTTW for “Windows to the World.” But the station that takes home the prize for the best four-letter combination is a sports radio station out of St. Louis that chose the name KRAP. Now that you know why radio stations do this, check out these other explanations for things you’ve always wondered about.

[Source: Primer]