Does anyone know what the yellow means on this M1 helmet? 

A P-47 of the Brazilian Air Force. Per Wikipedia, "During the Italian campaign, the "1º Grupo de Caça da Força Aérea Brasileira" (Brazilian Air Force 1st Fighter Squadron) flew a total of 48 P-47Ds in combat (of a total of 67 received, 19 of which were backup aircraft). This unit flew a total of 445 missions from November 1944 to May 1945 over northern Italy and Central Europe, with 15 P-47s lost to German flak and five pilots being killed in action. In the early 1980s, this unit was awarded the "Presidential Unit Citation" by the American government in recognition for its achievements in World War II."   I saw this Jug in person (along with a bunch of other great FAB aircraft and associated exhibits) when I visited the Museu Aeroespacial just outside Rio de Janeiro.  I think it's since been stripped of paint down to a polished aluminum finish.

Thanks!  My three ships sailing in was a stretch!  So the Col Robert T Cronau listed as Commander in 1945 was my Dad’s father.  Pretty sure this lighter belonged to my Dad, hence the Robert T Cronau, Jr.  Dad left the service right after the war, I think his highest rank was Captain. I don’t think my Dad served in Panama.  Dad scratched his name and the following things on the back of his wings: Lieut Cronau, CBI 7Mar 1945, Karachi India 1945, Philippine Is January 1946.  I do have a gold ring that belonged to my Dad that has a Mayan looking Indian face on the front.  I don’t know what significance Mayan culture had for him.   His dad, the colonel, also served in Panama between wars and my Dad spent time there as a child.  I kind of thought the cigar like thing on the cart was a bomb and my grandfather was in the 20th Bombardment Squadron at some point.  Dad flew cargo into Burma and then fighter planes in the Phillipines as the war wound down.  This is very curious.  Except for the RTC Jr, all the references pertain more to Granddad than Dad.  Oh well, they are both long gone and never talked about these things.  I attached the uniform patches that belonged to my Dad.

Spectacular!

Salvage operation is equal to  souvenir hunting? I can see combining the two activities.

Any chance of a better close up of the photo, very unusual wings. 

He also appears to be wearing jump boots in the photograph.    

XXVI Fighter Command   Constituted as XXVI Interceptor Command on 28 Feb 1942. Activated in the Panama Canal Zone on 6 Mar 1942. Assigned to Sixth AF. Redesignated XXVI Fighter Command in May 1942. Engaged in patrol operations in the defense of the Panama Canal. Inactivated on 25 Aug 1946. Disbanded on 8 Oct 1948.   Groups. 16th: 1942-1943. 32d: 1942-1943. 37th: 1943. 53d: 1942.   Stations. Albrook Field, CZ, 6 Mar 1942-25 Aug 1946.   Commanders. Brig Gen Adlai H Gilkeson, 6 Mar 1942; Brig Gen Russell E Randall, 17 Aug 1942; Col Willis R Taylor, 16 Oct 1943; Col Robert T Cronau, 15 Jun 1945-unkn.   Campaigns. American Theater. Decorations. None. Data from Air Force Combat Units of World War II By Maurer, Maurer, Published 1986

The lovely silverwork on that lighter is typical of Central American motifs (Mayan)   6th Air Force   The 6th Air Force was first constituted as Panama Canal Air Force on October 19, 1940 and activated on November 20, 1940.     The 6th AF was re-designated as the Caribbean AF in August 1941, and then 6th AF in February 1942. Primary responsibilities included Panama Canal defense.

Very unusual wing.   I wonder why it was made.