Thanks Pepe that you think it could be possibly be deoxit which is what I surmised too.
The reason I was asking is some guy is adamant that he thinks it's black paint used to mask excessive wear. I asked him if he was serious, which he was, and when I asked him would speakers connects be subject to excessive wear to the point that one would apply black paint to hide supposed excessive wear he couldn't answer me. The guy is a nut.