What forms of checks are undertaken to verify signatures?

Law on Nationwide Referendum adopted on 14 March 2003, Article 63

http://pkw.gov.pl/g2/i/00/8.pdf (in English - but not updated)

http://isap.sejm.gov.pl/DetailsServlet?id=WDU20030570507 (in Polish – the Parliament’s website)

Law on the manner of executing legislative initiative by the citizens adopted on 24 June 1999, Article 12

http://www.sejm.gov.pl/prawo/inicjat.htm (in Polish - the Parliament’s website)

Incase of reasonable doubt as to the correctness of signatures submitted with thereferendum request or citizens’ proposal, the Speaker of the Sejm can ask theNational Electoral Commission to verify them.