What is "AA6E"?
AA6E is an amateur radio station callsign, assigned by the U.S. Federal Communications Commission. "AA" is one of the prefixes assigned to every licensed radio (and television) station. You are probably more familiar with other U.S. prefixes, such as "W" or "K".
The numeral "6" indicates the FCC district -- in this case, California, where I originally got my license. (A native Connecticut license would have a "1", meaning New England.)
An FCC amateur radio ("ham") license nowadays requires a formal application and passing a written examination covering a certain level of electronics and radio theory along with knowledge of relevant government regulations. Up to 2007, hams also had to pass a Morse code test, but that is no longer required.
For more details on ham radio, check What is Ham Radio?