Actually, timr and roffman are both right. There's a loophole in the financial responsibility law that allows mopeds to roll uninsured, but by signing that form you're testifying to having insurance. So far the only ways around this are to 1) get insurance or 2) refuse to sign the form.
I know a couple people who, after arguing with the poor staff at the local BMV got away without signing it. With my motorcycle policy I can tack on up to two mopeds and still be at the minimum rate. If it's free I might as well ride insured.