Possibly done by a local police department for ID. This was commonly done in parts of California during the early '70s, when a bicycle license was "required".... They'd stamp the # anywhere, without thought.
The sleeve looks like it may be a business card...?
Duane Kennard Los Angeles, USA
On Oct 29, 2005, at 10:28 AM, John Waner wrote:
> Hi Dale
> I was shocked when I first saw that number stamped into the down
> tube but i just figured that was how some builders did it. Now I
> hope it just wasn't some one recording their phone number. What I
> have been waiting for is for some comment on what might be behind
> those holes in the BB. Could it just be some form of extra sleeve
> to keep dirt out of the BB.
>
> John Waner
> Huntington Beach, CA.