Hi everyone, It looks like PMD to me, but would like some other thoughts. When i compared the 7 to other 1979 it much shorter, and to the right of the chin is what looks like a horiziontal S mark, Not sure if its damge or not the mark next to chin doesnt show any lifting of metal and looks to be stamped as it is rasied. Unfortuantlly it is hard to tell from the stain on the coin.
I don't want to give you the wrong impression (pun intended) but I'm going to take the position that the "S" isn't really an intended "S" but rather a consequence of erosion on the coin. As for the 7, the upper portion of the seven looks defined and not looking like it was broken off from the die before being struck, so I'm going to say it's a normal 1979 cent. Others who are more insightful and knowledgable may offer better insight than mine though.
The only thing I see for sure on that coin is corrosion. That is bad enough I cannot make anything else out.