Here's the straight skinny on the USAF "Mike" call sign. I was a Special Operations (SOG) O-2 FAC operating out of Ban Me Thout East Field, SVN (BMTE) from April- Sept 1969 and then ALO until 1 March 70. I used a "Mike" call sign but I was not part of the Mike Force operation. I had a more clandestine mission not known by many at the time as we were operating in neutral Cambodia and had been for quite some time.  
  Overall, the "Mike" call sign belonged to the II Corp 5thSF O-1 and O-2 FACs that supported the Vietnam in-country Mobile Mike Forces starting about 1965 until the 5thSF left Nam in 1971. There was a 5thSF/ALO at Nha Trang assigned to and station at the 5thSF/HQ at nearby Camp McDormett beginning in Jan 1966 and he was the senior officer in charge of all 5thSF FACs. The Mike Force of USASF and CIDG troops operated throughout all Corps as needed. When in the II Corp area, their Mike Force ALO was at Plieku with FACs dispersed to outer FOLs. That is what your original call sign list showed but there were other "Mike" FAC operations and related call signs.

"Mike" as a cover call sign  to match the Mobile Strike Force call sign to mask the Top Secret operation in Cambodia from the Press. Worked like a charm.