I'm looking for a auto insurance company that the policy number starts with ABT?

Meaningless. I worked for insurance companies for 30 years and there was never any correlation. Company can use any prefix they want. Even among a single company, you can have numerous policy prefixes due to company classification. Usually the prefix is policy related-WC Workers Comp, HO-Homeowners, CMP-Commercial Multi Peril. ABT? Sure it's not ABI Possibly Auto Bodily Injury?

Why would you be doing this? Anytime there is a claim with insurance.. you would have other information about the policy holder (including the name of the insurance company) before you would have the policy number.

We see quite often where people are in an auto accident, and in exchanging personal information forget to write down the name of the other person's insurance carrier.

To the OP - assuming this is the case, I suggest you contact your own insurance company if you haven't already done so to report the accident and provide them with the info you have. You should do this even if the accident was not your fault. They can then follow up with the other person.