You might know the name Wedgwood from your grandma's china cabinet, but Josiah Wedgwood, who is best known for making fancy British pottery, was also heavily into the abolition movement. In 1787, he took the logo and catchphrase from the Society for Effecting the Abolition of the Slave Trade and used his sculpting skills to turn it into a medallion. (Source)

These medallions got crazy popular and ended up everywhere: in jewelry and on household goods, for instance, in both Great Britain and the United States. It's probably the most famous anti-slavery symbol, and it was originally intended to strike at the conscience. Douglass references this catchphrase when he refuses to argue whether or not slaves are people.