Buzz numbers were placed on USAF aircraft in the late 40's. This way it would be easy to record the number of an aircraft that flew under a bridge or buzzed a town. In 1963/'64 time frame buzz numbers were removed because it was found that someone sitting on a hill top or parked on a road could record the serial numbers of all aircraft assigned at a base. They would be able to have an accurate account of the aircraft and the amount that each aircraft flew. It would also give them an idea of mission capable aircraft at a base.
Over seas bases were the first to remove the buzz numbers, followed by TAC and SAC but ATC (allergic to combat) bases kept their buzz numbers longer. Something about not trusting student pilots.
Berny
Phormer Phantom Phixer 
On the bench
TF-102A Delta Dagger, 32nd FIS, 54-1370, 1/48 scale. Monogram Pro Modeler with C&H conversion.
Revell F-4E Phantom II 33rd TFW, 58th TFS, 69-260, 1/32 scale.
Tamiya F-4D Phantom II, 13th TFS, 66-8711, 1/32 scale. F-4 Phantom Group Build.