Start with what the marking has to do
Whatever it is made of, the federal marking for a commercial motor vehicle in interstate commerce is the same: your legal name or single trade name as on your MCS-150, plus "USDOT" and your number, on both sides of the power unit, in sharp contrast with the background, legible from 50 feet in daylight (49 CFR 390.21T).
Are magnets acceptable under that federal rule? The parts of the rule we have verified cover what must be shown and how readable it must be. We have not verified a federal answer on magnets either way, so we do not make a federal call on this page. If you need a firm answer for your operation, ask FMCSA at 1-800-832-5660.
Two states that put it in writing
- Iowa: intrastate carriers may have the marking painted on each side, or use a removable device that meets the identification and legibility requirements and is securely placed on each side (Iowa Admin. Code 761-524.12). Magnets qualify if they stay put. Iowa intrastate numbers read USDOT 1234567 IA. See Iowa USDOT decals.
- South Carolina: the SCDMV intrastate DOT FAQ says a pickup under 10,001 lbs that only goes over 10,001 lbs combined when towing may use removable magnetic signs while towing. That allowance does not cover wrecker service vehicles. See South Carolina USDOT decals.
Anywhere else, check your state on USDOT decals by state before you count on magnets.
Where magnets make sense
- Leased, rented or borrowed trucks: nothing stuck to paint you have to hand back.
- Part-time work trucks: a personal truck during the week, a working truck on weekends.
- Waiting on permanent lettering: paint, body work or a wrap is still weeks out.
Where vinyl wins
- Full-time trucks. Vinyl stays on with no daily checks. Ours is premium outdoor vinyl rated 5+ years.
- Aluminum or fiberglass doors. Some newer trucks and vans have them, and a magnet will not hold. Vinyl sticks to clean, smooth aluminum and fiberglass too.
- Ribbed, curved or creased doors. Vinyl follows the surface. A magnet needs it flat.
- Theft. A magnet comes off in seconds at a truck stop or job site. Vinyl does not.
- Cost. Our vinyl USDOT set starts at $16.00. The magnetic pair starts at $34.95.
Magnets at highway speed
A magnet holds by full contact with flat steel. Wind gets under any edge that is not tight, over a body line, a dent, a trim strip or a corner bent in storage, and can peel the whole sign off. Use the flattest panel, press all four edges down, and check it before each trip and after every wash. A magnet lost on the road takes your marking with it.
Paint and care
- Pull the magnets at least weekly and wipe both the door and the back of the magnet. Trapped grit and moisture are what mark paint.
- Let both surfaces dry before putting it back.
- Take them off before an automatic car wash.
- Store them flat, lettering up, out of the heat. Do not fold or crease them.
- Fresh paint or body work? Ask your shop how long to wait before using magnets.
Size: the mistake that hurts both
The 50-foot test is the same for either material, and a magnet's size caps your letter height. By our rule of thumb, a line needs about 0.8 inch of width per character for every inch of height. USDOT 1234567 at 2 inches runs about 21 inches, so it fits on one line on a 24-inch-wide magnet. On the 18-inch-wide sizes we stack USDOT above the digits, which needs the taller 18 x 10 or 18 x 12. The 12 x 3 and 18 x 4 sizes are too small for a 2-inch USDOT line.
Our house minimum is 2-inch numbers and 3-inch names, which is shop practice, not a legal number. Long names may come in under 3 inches on a magnet. The proof shows the real letter heights. Leave off phone numbers and logos that crowd the required lines. Placement tips are in our DOT decal placement guide.
FAQ
Are magnetic USDOT signs legal?
We have not verified a federal answer either way. Iowa and South Carolina allow removable signs in the cases above. Otherwise, ask FMCSA or your state agency.
Will a magnet stay on at highway speed?
On clean, flat steel with all edges tight, a magnet holds well. On aluminum, fiberglass or body lines it will not. Check it before every trip.
How do I know if my doors are steel?
Put a fridge magnet on every spot the sign will touch. If it slides or falls, order vinyl instead.
Decals for this
Have your USDOT number and your legal name exactly as on your MCS-150 ready. Free digital proof before we cut, free U.S. shipping.
- USDOT Magnetic Door Signs, from $34.95: a matched pair for steel doors, sizes 12 x 3 up to 24 x 12.
- Custom USDOT Number Decals, from $16.00: the vinyl USDOT line, set of 2.
- Custom Truck Door Lettering, from $18.95: your company name in vinyl to go with it.
Lettering for your trade
Pages written for one trade's vehicle, customers and state rules: mobile dog grooming van decals, pest control truck lettering, handyman truck lettering. See every industry.
General information, not legal advice. Rules change — confirm current federal and state requirements with the FMCSA and your state agency before you operate. Our state summaries were verified against primary sources July 2026.
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