The joke is a pun on the word 'mint'.  Mint is another word for a print of a coin.  The phrase the word is used in is usually said 'meant to be' meaning 'fated' or 'destined' but the word 'meant' was replaced with 'mint' because it's a joke about coins.  No context, so that it the entirety of the joke.
Coins are mint to be .