On airport codes

Haven't we learned yet that the airport code is DEN, not DIA?
(DIA is actually the airport code for Dia Island in Greece.)
Speaking of airport codes, it has come to my attention that the code for Sioux Gateway Airport is SUX. Evidently, the Iowa city is making the code part of a new marketing campaign.
While at the Sarasota-Bradenton Airport, I noticed that the airport signs (see picture) welcome passengers to "SRQ," rather than mention either of the two cities the airport services.
Comments
The Hartford newspaper doesn't call Bradley International Airport BDL in its coverage, and I'm guessing the Toronto Star doesn't refer to Toronto Pearson International as YYZ. Rush fans, however, do.