DEAR MISS MANNERS: I own a shop where I sell fine paper goods. After countless coffee spills and food stains on merchandise, I posted a “NO FOOD OR DRINK ALLOWED” sign next to the front door. People still walk in with greasy pizza slices, drippy ice cream cones and overflowing cups of coffee. When I restate my policy and point to a tray where they can set their food or drink while they shop, they glare at me and storm out like I’m the bad guy. Is there a way to enforce my rule with no hard feelings? GENTLE READER: Signs indeed hold authority — and humans can conveniently blame them when enforcing the rules proves awkward.