Here's a little more info that would date your patch no earlier than 1946.
The Meritorious Service Unit Plaque was established by War Department Circular No. 345, dated 23 August 1944. The circular provided that military personnel assigned or attached to an organization were entitled to wear the Meritorious Service Unit Insignia on the outside half of the right sleeve of the service coat and shirt, four inches above the end of the sleeve. Additional awards were to be indicated by a gold star to be placed on the plaque. War Department Circular No. 54, 1946, provided that additional awards would be indicated by placing a golden numeral inside the wreath
This patch was nicknamed the "Toilet Seat".