Here in Iowa, there is no voter ID requirement as long as the name and address you give matches one in the book who is active, didn't vote early and wasn't issued an absentee ballot. (Signature matching has no part in any of this. You sign the book to attest to your eligibility—the poll worker mentions the oath at the top of the page—and to show you were there.)
If you're flagged inactive in the book (haven't voted in the past three? years), you must show an unexpired state-issued photo ID.
If the book shows you were issued an absentee ballot, you must bring it with you to be surrendered at the polling place.
The requirements for same-day voter registration are similar (proof of citizenship and residency).
If all else fails, you can vote a provisional ballot. It gets sealed in an envelope which will not be opened until your eligibility is verified (e.g. you show up the next day at the auditor's office with whatever you didn't have on Election Day).
Since this is all off the top of my head, I probably forgot or misstated something. But, we're required to attend training next week and there's a clearly defined process to follow at the poll.
While the process makes in-person voter fraud rather difficult, the questions I'll ask (again) at training are these: How much post-election auditing is performed to ensure the marks on the paper ballots match the numbers reported by the ballot scanners and beyond? And, who monitors the audits?
We seem to have a really good system. We are not a swing state. I read about these counties who have computer controlled ballots and who report that their votes are changed. I read recently that 17 counties will probably decide this election.