Forensic Ink Analysis used to detect fraud. - https://www.azolifesciences.com/article/Utilizing-Thin-Layer-Chromatography-in-Ink-Analysis.aspx - It is easy to tell if ink on a vote came from 2 different pens or if the ink on 2 different votes came from 1 pen. Either option proves fraud/invalidates.

1 pen's ink on 2 votes = Electoral fraud

1 pen's ink on 1000 votes = massive electoral fraud

That combined with trace evidence such as DNA and fingerprints.... arrests should follow.