Quote:First of all, the President is the Leader of The Military.  After taking the Oath of Office he theoretically is no longer a "civilian" in the way that an average citizen is.  That being said, there is no written "rule" or law that says the President is required to render and/or return a salute.

 

Second, the military salute is a sign of respect for the position or rank that a person holds.  Generally speaking, only officers are saluted and the junior ranking member (officer or enlisted) is the one that renders the salute.  It is customary to acknowledge the salute by returning the salute.  There are cases when this custom might be reversed such as a higher ranking person saluting a member that has been awarded The Medal of Honor.

 

Think of it in terms of saying "thank you" to someone.  It is customary and polite to say "you're welcome".