Bring the vinegar, water, sugar, salt, coriander seeds, peppercorns, and bay leaf to a simmer in a small saucepan. Place the radishes in a 16-oz. jar with a tight-fitting lid. Add the vinegar mixture and cover with the lid. Chill 24 hours or up to 2 weeks. Serve as a garnish for a gimlet, a martini, or a burger.