It appears to be DDD die deterioration doubling.It can't be a RPM since the process of hand punching mint marks ended a decade earlier,still a nickel.
Keep in mind that the mintmark was part of the OBV details taken from the engraving (i.e., the D was part of the engraving). Repositioned mintmarks ended in the late 80s, so it could not be double struck. It looks like there's some damage in that area of the coin, given the lost detail between the field and the rim. And die deterioration may have been a contributor as well.
