I was going through sone online pics. the other day and I ran across a wartime photo of the 357th F.G. lining up at the end of the runway for take off. The photo shows P-51s fron the 364th as well as one plane from the 363rd F.S. The one from the 363rd has the codes B6Y on the underside of the left wing. I have seen a lot of pics. but this is the first I seen with the plane codes on the underside of the wings. Was this a common practice or is this a one off?