Possibly French made or French style pin back catch.
88th ID – 313th Combat Engineers DUI, No Hallmark but the pin back safety locking style I believe is French. This could be entirely French made or made in that style by an Italian maker. Most likely made just after the war while 88th Division troops are stations along the Morgan Line and in Trieste. 1945-47.
Fine- excellent condition.
NOTE: I have two of these that came together, both in the same condition, and make.