Make sure your Magnetic Sign Surface is Metal
Magnetic signs are made to adhere to steel vehicle surfaces.
So with that being said, if your vehicle is steel through and through, than a magnetic sign will stick to it. There are, however, exceptions to the rule even on steel vehicles. If your vehicle has had any body work done to it there is a good chance that underneath the paint job could be a layer of bondo. Bondo is an auto body filler that is widely used for car repairs because of it's paint receptive qualities. Magnetic signs can't stick to bondo, so if you are unsure if your vehicle has even been in an accident or had automotive repairs before you owned it, spot check the vehicle before purchasing magnetic signs. A simple way to test for underlying bondo work that will negate the magnetic qualities of magnetic signs is to take a refrigerator magnet and stick it to the vehicle. If the refrigerator magnet sticks then a magnetic sign will stick.
Another thing to be wary of is newer vehicles, which are being made with less and less steel; or vehicles that are made for racing and contain a good amount of fiberglass in the body of the vehicle. Magnetic signs will not stick to fiberglass. And as stated above, if you are unsure if your vehicle is magnet receptive, run to the kitchen and grab a refrigerator magnet and test the area where you want to place a magnetic sign.
Aluminum is also another alloy that magnetic signs will NOT stick too. Aluminum is another light weight material that is commonly used for 18-wheeler tractor trailers or box trucks. If you need to advertise on those styles of vehicles you'll be limited to magnetic door signs only. Any signage that needs to go on the trailer of a tractor or boxed in area of a box truck will need to consider adhesive vehicle decals instead.
Always remember to store your magnetic signs properly as well to assure that they will continue to adhere to your vehicle properly. Improperly maintained and cared for magnetic signs that have dust and debris on the magnetic receptive side of the sign can impair it's vehicle adhesion qualities causing possibly magnetic sign fly-offs as well. Proper installation counts for a lot as well. If your sign is not properly installed it may fly off as well even though it appeared to be sticking to your car. Please see our Magnetic Sign Care & Installation page for more detailed information on magnetic sign maintenance, installation and care.