1820s "T Porter" slave button (from Antigua, British West Indies), sewn onto the outer clothing of slaves -- used to identify the owner of the slave.
-- The Chillicothe Recorder (OH, dated Aug 23, 1815). Inside page headline with report on live slaves being thrown overboard from a slave ship, while shackled together. I have heard anecdotal stories of this but this is the 1st reference I can find to it actually having been done!
-- 1818 edition of Niles Weekly discussing the "Treatment of Slavery in Maryland".
-- Vintage engraving of a "Slave Felucca on the Coast of Africa", 1852.