Does placing a 'no valuables inside' sign in a car window deter break-ins?

All these labels do is "maybe" at best for professionals who look for other clues prior to acting on a target vehicle to a sound no for any Methhead. All the other results will be in between. BTW, LTC (Join to see) comment goes further. We'd call those things "Hit Me Stickers" as having them tend to make you a target for insurance fraud types. They set up a minor accident, claim lifetime disability, and then settle for somewhere in between.

A friend and I both parked under a bridge near the Pennsylvania RR station in Baltimore while attending prelaw. He drove a '47 Ford coupe and I drove a late model Mercury. I always left the doors unlocked and a dollar bill in the glove compartment. He locked his car. My windows were never broken and I only had the dollar taken once. Another time I found an extra dollar. My friends car was broken into several times and lost a flashlight and a box on book matches.

I laugh when I see that notice from AAA and an insurance company sticker like AAA on the car making it look like you have auto insurance.. That does not mean anything. Just keep your items in the trunk or hidden from view.