Yep, looks like gum or glue. Other coins were pressed against it to give those reverse-indented images. It's ordinarily a bad idea to clean coins, but you might have a hard time even spending this one if you don't.
Your coin is from before 1982 and thus made out of 95% copper as opposed to 83 and above which are copper-plated zinc. 99 is referring to 1999. If yours was a 1999 it'd be worth a decent amount since it would be a wide AM. EDIT: There are also copper-plated zinc 82's. They did the switch that year so there are both types for 1982.
Ya looks like a 1980- something. 92, 98,99 and 00 in case you did not know are good to search for close and far AM in America of course.