Frankly I'm going to fall on the American side of not wanting to disclose my SSN for freebie income. I'm not a fraud, spammer or Scammer, but neither do I wish to open myself up for Indentity theft.
Even here in the USA it's not reccommended that you give out your SSN willy nilly because of the growing problems with Identity Theft. As has already been noted by someone else, as freelancer's it is our own responsibility to report our income, not ShareCG's as we are not Direct Employees of their business.
Frankly, the income I've made off my freebies last year doesn't even add up to a significantly reportable income amount. I wouldn't report it any more than I report income I make from a Garage Sale.
It is a miracle that curiosity survives formal education. - Albert Einstein