30. Where a simple signature on a blank paper is delivered by the signer in order that it may be converted into a bill, it operates, in the absence of evidence to the contrary, as an authority to fill it up as a complete bill for any amount, using the signature for that of the drawer or acceptor, or an endorser, and, in like manner, when a bill is wanting in any material particular, the person in possession of it has, in the absence of evidence to the contrary, the authority to fill up the omission in any way he thinks fit.

R.S., c. B-5, s. 31.