Guard Mount refers to two things. The first is the actual forming (mounting) of a military security group called: the Guard. The second is the bugle call which was used to signal the formation of the group.
Guard mount refers to a pre-shift official formation among designated United States Air Force Security Forces members. This meeting is usually held after all security personnel have "armed up" or received their weapons and equipment for the shift. During the formation the flight leader (known as the flight chief) will discuss topics such as current squadron, base or other air force level news, current terrorism warnings or military intelligence, and weapons, vehicle and ground safety. Members also will be inspected and assessed on their appearance, uniform and checked for required equipment. When held in a deployed combat threat environment, guardmount is somewhat akin to US Army Pre-combat Checks and Pre-combat Inspections, PCC and PCI respectively.
Guard Mount is a bugle call which sounds as a warning that the guard is about to be assembled for guard mount.