The mint mark is the tiny letter on a Kennedy half ... but that's probably not worth running to eBay for. Kennedy bicentennial half-dollar coins, minted in 1976 to commemorate the 200th birthday ...
The reverse side showcases an image of the Liberty Bell superimposed with the national motto, "E PLURIBUS UNUM" and the words "USA" and "QUARTER DOLLAR ... mint mark on the obverse of 1976 ...