For the most part no...but there are exceptions to that rule when magnetic signs are not installed properly.
If your magnetic sign is maintained and installed properly, then the risk factor of losing a magnetic sign is fairly non-existent, at least while driving. Magnetic signs utilize vehicle grade magnetic material that has an 86 lb. pull per square inch. So essentially our magnetic signs are manufactured with high-quality magnetic sheeting that is meant to stay on your vehicle and high speeds. Magnetic signs that sit on a vehicle properly will not fly-off. However, if the magnetic sign is placed over any obstacles, that will allow air underneath it's surface, then you do run the risk of losing a magnetic while on the road.
Common vehicle obstacles that contribute to most magnetic sign fly-offs are door jams, vehicle emblems, door handles, contoured body styles or vehicle concaves. When a magnetic sign is placed over any of these vehicle obstacles, a chance for air to get up under the magnetic sign material, which can cause a potential magnetic sign fly-off and result in the loss of your magnetic sign(s). The only way to eliminate this problem is to make sure you are ordering a magnetic sign size that will correctly fit your vehicle. So first and foremost we recommend measuring your available "FLAT" surface area of your vehicle, before ordering your magnetic signs, to assure a perfect fit. Ill-fitted magnetic signs, that do not sit flush on the vehicle, can and will fly off so make sure you order an appropriate size for your vehicle.
Maintenance is also an important key to not losing magnetic signs and reducing the risk of a magnetic sign fly-off. Always make sure to gently clean the application area of your vehicle and the magnetic receptive side of the sign before installation, to remove any dust or debris that may have accumulated, which can cause adhesion problems and result in the loss of a magnetic sign. And make sure that when you storing magnetic signs that they lay completely flat without laying over any objects. If left draped over an object for too long a magnetic sign may conform to the shape of that object, which when put back on your car, won't be laying flat on the surface of the vehicle which can lead to fly-off risks as well.