6:47 AM
today I learned that at some point US Customs used to covertly install transponders with code 1236 on aircraft suspected of being used for illegal activity so they would show up on the scope with "SUSP" in the data block
this tracking method is apparently obsolete and not in use as of 2009
(FAA systems recognize and tag up certain beacon codes, 7500-Hijack, 7600-Radio failure, 7700-Emergency, 7777-Military intercept, and apparently formerly 1236-Suspect aircraft)
(I guess the procedure when you observed a suspect aircraft moving would be to... call US Customs?)