What an MCS-90 endorsement is

It is an endorsement, not a separate policy

MCS-90 is the prescribed endorsement in 49 CFR 387.15. When it is attached to a liability policy, the insurer agrees to pay, within the public-liability limits, any final judgment against the insured for bodily injury or property damage resulting from the negligent operation, maintenance, or use of motor vehicles subject to the financial-responsibility rules, even if the policy would otherwise exclude the loss.

The point of the endorsement is public protection. It exists so that a gap in the policy (an uncovered auto, a denied driver, a radius exclusion) does not leave the public without a filed source of payment. It does not create a new pile of money above the filed limit, and it does not decide who was at fault.

What it does not do

MCS-90 is not cargo coverage. It is not a promise that the insurer will defend every claim. Courts have spent decades arguing about whether it applies to a particular vehicle or a particular insured. Those arguments are case-specific. The endorsement form itself is public and short. Read the form, then read the policy.

The carrier lookup on this site shows the federal insurance filing (insurer, form, filed limit) as of the date of the query. That filing is how you learn which insurer likely issued the MCS-90. The endorsement copy lives with the insurer and the carrier, not in the Motus table.

Preserve the policy file

If a crash may implicate MCS-90, the preservation letter should go to the insurer named on the filing as well as the carrier. Ask for the policy, every endorsement including MCS-90, the BMC-91X, and the declaration of covered autos. Those documents have no useful federal retention clock of their own. The letter is what keeps them.