That's the three-letter airport code for Sioux City, Iowa.

Fun story, After decades-long fight, Iowa airport embraces unflattering identifier SUX - Metro

SIOUX CITY, Iowa (AP) - City leaders have scrapped plans to do away with the Sioux Gateway Airport's unflattering three-letter identifier - SUX - and instead have made it the centerpiece of the airport's new marketing campaign.

The code, used by pilots and airports worldwide and printed on tickets and luggage tags, will be used on T-shirts and caps sporting the airport's new slogan, "FLY SUX." It also forms the address of the airport's redesigned Web site - www.flysux.com.

Now if only I had a reason to go to Sioux City.....

HT: Sarah Skwire at Liberty Fund.