Wiktionary
touch piece
n. (context now historical English) A coin or medallion given to someone in Britain after they had been touched by the sovereign as a cure for the king's evil.
Wikipedia
Touch piece
A touch piece is a coin or medal believed to cure disease, bring good luck, influence people's behaviour, carry out a specific practical action, etc.
What most touch pieces have in common is that they have to be touched or in close physical contact for the power concerned to be obtained and/or transferred. Once this is achieved, the power is permanently present in the coin, which effectively becomes an amulet.