What is a voting finger?

Answer 1

In some countries, those who have voted have their fingers dyed to confirm the fact and are not therefore eligible to vote a second time

Answer 2

A voting finger is a colloquial term used to describe holding one's finger inked after casting a vote in an election. It is a symbolic gesture to show that an individual has exercised their right to vote. The ink is typically applied to the index finger as a way to prevent double voting.