Signs as deterrents of illegal parking in spaces designated for individuals with physical disabilities.

Dunlap et al. (1991) tested a cheap way to stop people from parking in disabled spots. They put up a sign that said 'concerned citizens are watching.' Then they counted how many drivers still parked there.

The team used an ABAB design. They added the sign, took it away, added it again, and took it away again. Each step lasted several weeks.

When the sign was up, illegal parking dropped from about 69% to 27%. That is more than half.

When the sign came down, bad parking shot right back up. The pattern repeated every time they changed the sign.

Mueller et al. (2000) did almost the same thing in public bathrooms. They posted a sign and graffiti vanished. When the sign left, the scribbles returned. Both studies show that a simple posted sign can act like a giant prompt.

Hsieh et al. (2014) pushed the idea further. They put signs in a hospital kitchen and staff kept dishes in the right spot for four straight months. Their longer follow-up tells us the effect can stick around.

Gaylord-Ross et al. (1995) moved a free condom bowl to a busier spot and tripled use. Like G et al., they changed one passive thing in the room and watched behavior jump. Together these papers say: tweak the setting, not the person.

You can cut rule-breaking fast by adding a short social cue. No staff, no tokens, no data sheets. Try a friendly sign that reminds people someone is watching. Place it where the problem happens. If the behavior returns, move the sign or change the message. One sheet of paper can do the work of a full intervention.