A quick search shows that P-47s from the 27th FG had letters on the tails. There is a painting that shows P-40s and is signed by members of the 27th FG and Lt. Ray Knispel is one of those who signed the painting. I can't make the link work so here's the Googler
This is my dads p47. Shot down in the south of France behind enemy lines. Took 3 week of running with French underground to get back to base. He flew 88 missions