What forms of checks are undertaken to verify signatures?

Law on Referendum of Georgia(2003)

http://www.venice.coe.int/docs/2003/CDL(2003)077-e.pdf

Article 12. Adjudicating theresults of collecting signatures

1. Completed signature papers are sent to the initiative group, whichdefines the summarized data about the results of collecting signatures andsubmits it to the Central Referendum Commission along with the signature papersno later than 3 months after receiving the registration card.

2. Central Referendum Commission checks the received materials and if theydo not contradict with the requirements of this Law, the Commission submits itsconclusion and the request of the initiative group about the conduct ofreferendum to the President no later than 1 month after receiving thematerials.

3. If it is found out that one and the same voter had signed the requestform for the conduct of referendum twice or more times, all the signatures willbecome invalid.