Take cues from your surroundings. The more exposed an area is, ie. near a sidewalk, the easier it is for scammers to place fraudulent QR codes on them. Meanwhile, at restaurants, hotels, or in gated parking lots, there is less foot traffic and less exposure to risk. Although, QR code fraud can happen anywhere.
Pay close attention to branding, colors, appearance, and even wear. Does a QR code sticker look brand new while the signage behind it is old and faded? Red flag!