Here's a Mystery for you

The Timekeeper Conspiracy - Simon Hawke

A time travel adventure set in the 2600s.

 

It felt strange to be saluted in the corridors. As a noncom, Lucas had never insisted on military protocol, or as most soldiers called it, "mickey mouse."

 

It was an age-old expression and no one seemed to know where it had come from. Lucas had once queried the data banks on it, only to discover that the information was classified.

 

Classified! -- kind of makes you wonder doesn't it.  I can come up with several scenarios which serve as an explanation.  But not one of them makes any sense.