I'm a big fan of this tradition. I don't believe the superstition, but it's a nice ritual in the knife-making / gifting process, and it always sparks conversation.
When I make a knife for someone, I ask for a coin in return. It can be any kind of coin, but I ask that it be from their country of origin or residence, if possible. When I get the coin, I grind a flat space on one side, roughly engrave the name of the recipient and the year of the transaction, punch a small hole in it, and add it to the others hanging on a chain above my workbench. Most are Canadian, but there are a few international coins in the bunch.
All the best,
- Mike