The 1979-S type 2 through the 1981-S type 1 (to include all 1980-S) are have the same style mint mark. The changes were between the 1979-S type 1 and 2, and again between the 1991-S type 1 and type 2. I don't believe there are any variant 1980-S mint marks. Could be environmental damage. I don't think we can help more than that without a picture. Just make sure the picture is under 300K and you shouldn't have any problems uploading.