Pit (or not!) the cherries. In a small saucepan, heat the maraschino to a low simmer; do not boil. Remove from heat, and add the cherries. Once cool, transfer to a pint mason jar and store in the refrigerator. They're ready within a few days, but will stay for months in the fridge.
You could use kirsch in lieu of the maraschino, but if so you may want to dissolve 1/4 cup sugar before adding the cherries.