This is a fairly easy question to answer when you sit down and decide where you see the USDOT numbers 12 months from now. Are you using the vehicle for business on a temporary basis? Are you leasing a semi? Do you have a well established trucking company and own your fleet? Figuring out what your short to long term use for your display numbers will help you determine which option to go with.
Lets start with the pros and cons of using magnetic signs to display your USDOT numbers.
Magnetic signs are a great option for those that lease vehicles or make use of a personal vehicle for business that would require the USDOT number to be displayed on the vehicle. Instead of have a permanently affixed USDOT number on your vehicle, you can easily remove your magnetic signs and store them for future use. Magnetic signs are perfect for trucking companies and logistics businesses that lease semis or delivery vehicles. Using a magnetic sign for display is completely legal and 100% USDOT compliant. The 2" minimum lettering height requirement applies to the use of magnetic signs as well.
The cons of using magnetic signs for the display of your USDOT information are few. You are limited to steel as the surface you can apply a magnetic sign to. They do not stick to fiberglass or aluminum. This unfortunately eliminates late model Ford F-Series trucks as they are now using aluminum in their body panels. Another con is that they don't look as professional as vinyl decals when used to display your required USDOT information.
The preferred and more common media used to display your USDOT number and information is die-cut vinyl lettering. Vinyl lettering consists of numbers and letters that are cut from a solid sheet of 7-year vinyl. The material that is not used is then 'weeded' out of the solid sheet, application pre-mask tape is applied to the lettering and then is used to remove the vinyl from the carrier sheet and applied to the surface of the vehicle. When it is all said and done, you have a very professional application that appears as if the lettering was painted directly on the surface of the vehicle. Vinyl lettering also comes in reflective which will gain your USDOT number additional visibility at night.
As far as cons go, the list for using vinyl lettering for your USDOT numbers is short as well. With vinyl decals, the application is more permanent. In order to remove the decals from the surface of the vehicle, one must apply heat and solvent. This virtually disqualifies utilizing this media for temporary use. Removing the lettering is difficult and if done improper, can damage the surface of your semi or logistics vehicle.
In conclusion, vinyl lettering and magnetic signs are a great way to display your USDOT number information but choosing which to use depends on a few factors. I hope you found this information useful in that endeavor.