Lay out the peanut butter cookies on a parchment-lined cutting board or baking sheet.
Squeeze about a ¼ teaspoon of decorating icing in the middle of the top of the cookies. It's okay if it's not perfectly neat.
Press one chocolate kiss on top of the icing, carefully pushing the icing around the base of the kisses.
Place 1 M&M chocolate candy on the front of each kiss in the icing or sprinkle some Halloween sprinkles onto the icing.
Serve at room temperature. Store in an airtight container on the counter at room temperature or in the fridge to keep the chocolate from getting melty.