A scrutineer is a person who oversees voting in an election, or counts the votes, in order to make sure it is all done correctly.

Rules vary but typically each candidate or party may have one scrutineer or poll-watcher per constituency or precinct where voting is taking place. They are often required to refrain from contact with voters, wear or display political slogans, or otherwise exert influence on the conduct of the election while it is taking place.

Synonyms

The name Poll-watcher is commonly used for this role in the United States