by a show of hands meaning

• [American slang]
  [of a vote taken] expressed by people raising their hands.
    We were asked to vote for the candidates for captain by a show of hands.
    Bob wanted us to vote on paper, not by a show of hands, so that we could have a secret ballot.

• a show of hands:    [American slang]a ...
• show of hands:    A vote by holding ...
• hands:    Noun: hands & ...

Examples

1. the issue was decided by a show of hands
2. by a show of hands, how many of you can already read
3. by a show of hands only ..
4. by a show of hands only
5. Samaranch proposed the expulsions be confirmed by a show of hands.