Welcome to the forum!
I'll move this one to "DS1 Only" as this is the kind of issue that will plague the older DS1s, those built before '71.
Older boats do indeed not have a standard HIN. Many had a small metal plate that contained the relevant number; some years had that riveted to the wooden coaming at the transom (in that case there may be rivet holes in the wood). Other years had a plaque riveted to the bulkhead inside the cuddy.
Look at the thread on DS1 design changes to help you identify a likely model year (or post detailed pictures). Then approach your DMV or other state licensing office and, stating the year you think it was built, ask them how to acquire an official HIN. You may then have to add that to your boat. (There should be some older posts here where people discuss similar issues).
Check your sails for a sail number. With luck there's one. Become a member of the DSA (
Day Sailer Association) and contact the secretary to "register" that number to you.
Some people have reverse engineered a pre-HIN hull number plate, but usually when they had some idea what the actual hull number had been - in the early years, the "hull" number was not model specific, but counted all the hulls by the same builder, the "sail" or "class" number was assigned separately and was model specific. Nowadays, the latter is part of the HIN as HINs are model-specific, with a prefix for builder and date.
Let us know what you find out about the rules and processes in your state.