If you or your company operates a vehicle for commercial purposes, that transports passengers or hauls cargo from state to state for commerce, you must register with the Federal Motor Carrier Safety Administration (FMCSA). Upon completing your registration, you will be supplied a registration number and you will need to display the US DOT number on your vehicles. Your unique USDOT number will be your individual identification number for any company safety audits, vehicle inspections, accident reports and compliance reviews. This number will be required to be posted on both sides of your vehicle and must be visible from a minimum of 50 feet away. A general rule of thumb is that lettering that is 2” or taller will meet this visibility requirement for your US compliant DOT numbers. Some states and municipalities do require a larger number than the US Department of Transportation (visit our Regulations page to view the regulations by state). You can install the numbers on the vehicle using adhesive vinyl stickers or magnetic signs so long as the decals or magnets are contrasting, meaning the color of the numbers contrasts from the color behind them to allow for easy visibility. For the US DOT Stickers, the vehicle paint color should contrast with the color of the stickers. For the magnets, you will want to choose a light color for the background, and dark color for the numbers (or vice versa).