Both the 518th MP Bn. and the 509th MP Bn. were assigned directly to First Army for Operation Neptune & the marking shows up in Normandy photos shortly after D-Day. Just a guess - perhaps this is a symbol for First Army Provost Marshal and might have been used by army-level MP units.
AWESOME PHOTO !!!
What reference did you use in finding this information? (Thats the kind of material I have been looking for.) I have thought about trying to format a spreadsheet with listings & assigments for MP units in the ETO; but time & computer skills are a premium with me.
Can you please check the list again, and see if there is mention of the 783rd or 713th MP Battalions? Both were supposedly assigned to 1st Army, but parceled out at various times. Neither wore the emblem you indicated, so it may have been just the 509th & 518th.
C Co./783rd MP - Passed to 5th & 6th ESB on 6/9/44. Landed 6/10/44 and cleared traffic from Omaha Beach.
D Co./783rd MP - Passed to 1st ESB on 6/3/44. Landed 6/10/44 and cleared traffic from Utah Beach.