小米新的回复是这样婶儿的：You will need to write a short letter stating your mother is your sponsor, take the letter to a government official , notary or a lawyer. They can witness the signature on the separate letter.|
I cannot use the scanned letter as proof of funding.
Your Mother's signature must be witnessed by an official notary or government official. there must be an official notary stamp on document. She can write a separate letter if they will not sign the form.