615th Antiaircraft Artillery - Canal Zone
You have a sun helmet worn by a member of the above unit. You'll note that it's constructed so as to allow air to circulate about the scalp as well as provide shade. The shield you refer to is the distinctive insigne - unit crest, if you will - of the 615th. The unit was first activated as 615th Coast Artillery (Antiaircraft) Regiment at Fort Clayton, Canal Zone in April 1942; redesignated 615th Antiaircraft Artillery Group in September 1943 and inactivated in January 1946. Their mission, as implied by the designation, was to provide protection against possible air attack.