It is the sheet number, repeated from the face of the note where it would occur in normal size numerals, on the 1894 issue. For a good example of this, look on page 16 of the current edition of Canadian Bank Notes, where face and back of the illustrated 1894 $5 note both are numbered 76058.
Charter numbers were not used in Canada. The closest thing to a charter number was the bank's ranking in government published bank returns, which appears as part of the logo on machine-signed notes starting after the enabling legislation of 1913 - - but I digress.
