Mail-in ballots that need to be reviewed because of signature discrepancies sit in boxes at the Miami-Dade County Elections Department in Doral, Fla., on Oct. 15. Signature problems are a frequent reason that ballots are rejected, though many states allow voters to fix those problems before Election Day.

DORAL, FLORIDA – OCTOBER 15: Boxes for Vote-by-Mail ballots that need to be reviewed due to signature discrepancies are seen as the Miami-Dade County Canvassing Board convenes ahead of the November 3rd general election at the Miami-Dade County Elections Department on October 15, 2020 in Doral, Florida. The canvassing board was verifying questionable voter’s signatures on the Vote-by-Mail ballots by comparing them to the signature on file. Voters have cast 149,683 Vote-by-Mail ballots so far and only 414 of those had been questioned. Voters head to the polls in Florida on October 19th for early in person voting for the November 3rd election where President Donald Trump and Democratic presidential candidate Joe Biden are facing off against each other. (Photo by Joe Raedle/Getty Images)