slaves were sometimes branded by their masters to prevent their escape; and so devotees to an idol god sometimes caused to be impressed on themselves the name or image of the divinity which they adored. Herodotus (ii. 113) mentions a temple of Hercules in Egypt, in which if any slave took refuge, and had the sacred brands or marks impressed on him (στίγματα  stigmata), he thereby devoted himself to the god, and it was not lawful for anyone to injure him. Many have supposed that Paul here says, in allusion to such a custom, that he had the name of the Redeemer impressed on his body, and that he regarded himself as devoted to him and his cause. {Albert Barnes' Notes of the Bible (Gal6:17)}