From your other posts I know that your are the proud owner of what you believe is a "late 60s" DaySailer.
Turns out, the standardized hull numbers (HIN) are a product of the early seventies.
Before that, manufacturers counted not the hulls for each model, but all their hulls. And they gave out a a "class number" which, because it is shown on the sail, is also called a sail number. These two numbers they punched into a metal plate that was screwed or riveted to some place on the boat.
The middle of the rear coaming, or the middle of the front flotation tank are two popular locations for the DS. These spots aren't really hidden, so if you can't find yours, then you are out of luck; your boat got separated from the manufacturers plate at some point.
Of the two numbers, the "sail number" is the more interesting one, because that's the one you might want to put on your sails. (Required if you ever want to race, or just so you can recognize your boat on a photo otherwise). Sometimes the state papers will contain a number, it's hit or miss whether that would be hull or sail number. Numerically, I'd expect a sail number for the late 60s to be above 2000 and up to perhaps double that. (See the history section for more details).
Sometimes, you may find an original sail (or one that has the original sail number still on it, if it was purchased new for your boat).
If you find a likely number you can contact the class association (DSA) at
http://daysailer.org and ask the secretary to find out whether the number is claimed by any "known" boat. If not, it can be assigned to you. (At that point, you might decide to join the DSA; your membership would help finance the server bill for this forum, for instance.)