Sentence:  ... and the freemen signified their approbation by an inscribed vote, and their dissent by a <WSD>blank</WSD>. 
Meaning of the word marked with <WSD> tags:  A document, paper, or form with spaces left blank to be filled up at the pleasure of the person to whom it is given (e.g. a blank charter, ballot, form, contract, etc.), or as the event may determine; a blank form (since the 16th century).