The DOT certification mark on a windshield is a small permanent stamp, often called the “bug,” that identifies who made the glass, certifies it meets Federal Motor Vehicle Safety Standard No. 205, and tells you which positions on a vehicle that piece of glass is legal to use.1eCFR. 49 CFR 571.205 – Standard No. 205, Glazing Materials Once you know what the three or four elements mean, you can read it in under a minute.
Where to Find the Mark
Check the lower corners of the windshield first, then the lower edge of the side and rear windows. It is not a sticker. Federal rules require the marking to be legibly and permanently applied in characters at least 1.78 mm tall, so it is etched or printed into the glass itself and sits against the dark ceramic border near the edge.2National Highway Traffic Safety Administration. Interpretation 1864y – Standard No. 205 Glazing Materials
A typical bug stacks several items together: the glass maker’s name or trademark, a vehicle manufacturer logo on original-equipment glass, the letters “DOT” followed by a number, a two-character code beginning with “AS,” an “M” number, and sometimes a date of manufacture. Not every element appears on every piece, but the DOT code and the AS code are always there because federal law requires them.
What Each Part of the Stamp Means
The DOT Code
The letters “DOT” followed by a numerical code identify the specific plant that produced the glass. NHTSA assigns this code after a manufacturer submits a written request to the Office of Vehicle Safety Compliance certifying its status as a prime glazing manufacturer.3eCFR. 49 CFR 571.205 – Standard No. 205, Glazing Materials – Section: S6.2 A marking like DOT-43 or DOT-287 points to one factory, which means every piece of glass carrying that code can be traced to its source. That traceability is what makes targeted recalls possible when a defect surfaces at a particular plant.
The AS Classification
The two characters starting with “AS” are the most consequential part of the mark, because they dictate where the glass may legally be installed. There are three:
- AS1 is laminated glass with at least 70 percent light transmittance. It is the only classification permitted for windshields, and it can also be used anywhere else on the vehicle.4National Highway Traffic Safety Administration. FMVSS Interpretation – nht74-2.34
- AS2 is laminated or tempered glass with at least 70 percent light transmittance. It is acceptable everywhere on the vehicle except the windshield.4National Highway Traffic Safety Administration. FMVSS Interpretation – nht74-2.34
- AS3 is laminated or tempered glass with no minimum transmittance requirement. This is the heavily tinted glass used on the rear of SUVs and trucks, and it may only go in positions not required for driving visibility.4National Highway Traffic Safety Administration. FMVSS Interpretation – nht74-2.34
One point often gets confused: AS2 is not always tempered. It can be either laminated or tempered so long as it meets the 70 percent transmittance threshold. What defines AS2 is that it cannot be used as a windshield. If you see AS2 or AS3 stamped on a windshield, that glass does not belong there, no matter how clear it looks.
The M Number
Below or beside the AS code you will usually see an “M” followed by a number, such as M119 or M256. This is the manufacturer’s internal model designation, and it encodes technical specifications like glass thickness, tint shade, and construction type. When ordering replacement glass, matching the M number to the original specification is how you confirm the new piece has the same weight, thermal properties, and optical characteristics that were engineered for that opening.
Feature Icons
Newer windshields sometimes carry extra symbols for special features. A small thermometer icon or “IR” marking signals a solar-reflective or infrared-absorbing coating designed to reduce cabin heat. An ear-shaped icon or the word “acoustic” indicates a noise-dampening interlayer between the glass plies. These do not appear on every windshield, but when they do, they matter for finding the right replacement. A plain laminated windshield will not perform the same as one with acoustic or solar-control properties.
Looking Up a DOT Code
You can verify any DOT code yourself. NHTSA runs a free public tool called the Manufacturer Information Database. Open the database, choose “Glazing” as the equipment type, and enter the numeric code from your glass.5National Highway Traffic Safety Administration. Manufacturer Information Database (MID) The results show the manufacturer’s name, plant location, and registration details. If the code returns nothing, or the listed company does not match the trademark printed on the glass, that is a reason to ask the shop that installed it for an explanation. NHTSA also runs a manufacturer helpdesk at 888-399-3277 for questions about specific codes.
Using the Mark When Replacing a Windshield
Replacement shops typically offer two tiers: OEM glass, produced by or under license from the vehicle manufacturer to the original specification, and aftermarket glass, sometimes labeled OEE for original equipment equivalent. Both must carry a DOT code and meet the federal minimum under FMVSS 205.1eCFR. 49 CFR 571.205 – Standard No. 205, Glazing Materials The federal floor does not guarantee identical thickness, curvature, tint, or optical clarity, and those finer details are where aftermarket glass can drift from the original.
Where the drift becomes a real problem is on any vehicle with a forward-facing camera behind the windshield for lane-keeping, automatic braking, or adaptive cruise control. Different glass bends light differently, so replacement changes what the camera sees, and the system needs recalibration after installation. That is a separate step from the glass mark itself, but worth asking the shop about before scheduling the job. For matching the glass, comparing the DOT code and M number against the original is the simplest check.
What a Missing or Wrong Mark Tells You
Every piece of automotive glazing legally sold in the United States has to carry this mark. If a windshield in front of you has no bug, or the bug is illegible, or there is no DOT code, the glass has no verified chain of testing behind it. You cannot confirm its shatter behavior, its optical quality, or its bond strength from the outside. Before accepting a replacement, take thirty seconds to look at the lower corner. A clean, complete stamp with a working DOT code, an AS1 designation, and an M number that matches your vehicle is what you want to see. Anything less is worth a conversation with the installer before you drive away.