The pin is a distinctive unit insignia of the 17th Engineer Battalion. Probably lost by a soldier on leave or a vet. The 17th was activated at Ft. Benning, GA in 1940 and served in WWII in North Africa, Sicily, France, and Germany. After the war they were stationed at Ft. Hood, TX and in Germany. They went to Saudi during Desert Shield/Storm. They were inactivated at Ft. Hood in 1996.