I worked passenger screening more than a decade ago. Back then we were told to question any police member carrying a firearm as to whether they were traveling on an aircraft and if that they were traveling then they were NOT permitted to carry firearm on board.
The question for me though......why was the officer traveling in uniform? Was he asked the question? If so, what did he say? This could be very nasty for him/her if the security guys did the right thing and he fobbed them off due to not wanting to go through the hassle of going back to the Airport station and surrendering his appointments.