What forms of checks are undertaken to verify signatures?
Bulgaria
Referendum - The National Assembly shall submit thesubscription of the Directorate General of the 'Civil Registration andAdministrative Services' in the Ministry of Regional Development andPublic Works, which immediately officially check the signatures. When therequired number of signatures is detected the verification should bediscontinued.
Act on Direct Participation of Citizens in Government and Local Government of29 May 2009, art. 13 (2), art. 51 (3)
http://?www.?lex.?bg/?bg/?laws/?ldoc/?2135636485 (inBulgarian)