Harlan Greene, an author and senior manuscript and reference archivist for College of Charleston libraries, said slave and free men’s tags are now valued artifacts. Square, round and diamond shaped, slave tags were numbered and listed the type of work a slave could perform.

http://www.postandcourier.com/article/20120529/PC16/120529101/rare-free-man-s-tag-taps-slave-era-history-in-charleston-sc