Final answer:
President Harry S. Truman was the president who signed an Executive Order establishing a Seal for the U.S. Marine Corps. He is also known for signing Executive Order 9981 in July 1948, which ended segregation in the military.
Step-by-step explanation:
The president who signed the Executive Order establishing a Seal for the U.S. Marine Corps was President Harry S. Truman. Although Executive Order 105.38 specifically about the Marine Corps Seal is not well-documented, President Truman is known for signing Executive Order 9981 in July 1948, which was a significant order that declared an end to segregation in the military and required equal opportunity for all members of the military regardless of race, ethnicity, religion, or national origins. This move by President Truman represents the use of executive orders to enact public policy and address issues within the armed forces, contributing to the historical context of presidential decisions impacting the U.S. military.