https://8ch.net/patriotsfight/res/62.html#q82
I looked up specifically USAF Ladder trucks. Here's one that's similar. NO LETTER in front of the number. I didn't see ANY that had letters+numbers. This is definitive proof for me, guys. THanks Q!
I searched, USAF fire truck, Ladder fire truck, Quint fire truck, United States Air Force Quint Fire Truck, United States Air Force Ladder Fire Truck and found some that had the word "Quint" in front of or on top of the number. But only one with a T in front like the other poster said. I don't think it's common at all.
I found a pic you can read on the door "United States Air Force"
I found it! I found another picture of the actual truck! This is from 2 days before the photo on the tarmac was taken. But this other photo in 2007 was taken of what I believe is the same truck and there is no number on it. So was it added very recently?
http://www.jba.af.mil/News/Commentaries/Display/Article/1514643/national-police-week-2018-remembering-the-fallen/