Section 88(2)(d) of the Electoral Act, 1992, provides for the printing of a serial number on the back of a ballot paper and on the back of the counterfoil in the smallest characters compatible with legibility. The number serves as an important security feature against the introduction of forged or counterfeited papers and as a control mechanism for the issuing of and accounting for ballot papers at an election.
The pre-1972 practice of noting a person's number on the register of electors on the counterfoil was discontinued following the case of McMahon v Attorney General – 1972 Irish Reports page 69 – where the Supreme Court ruled that that provision was contrary to Article 16 of the Constitution.