Polling officials must check whether the voter has already voted in the election. In principle, multiple voting can be avoided if the voters are properly identified and registered, and the voter lists are signed by the voter (and marked by the polling officials) when voters present themselves at the polling station and receive the ballot paper(s). However, in practice, there are instances in which voter lists were not signed by voters, or in which multiple similar signatures with the same handwriting were found on the voter lists. Stamping of identity documents or voter cards may also be used to indicate that voters have already voted. Stamping ballots or voting envelopes is an additional safeguard, and common practice in CoE member states, to ensure that additional ballots cannot be brought into a polling station.