Republicans and Democrats have long been concerned about how the vote will shake out in Arapahoe County - one of the key swing counties in an undecided state - and now they have one more thing to fear: an "I Voted" sticker.
More than 230,000 ballots last week were mailed to Arapahoe County's voters in envelopes that possibly contained a participation sticker that rubbed up against the ballot and in some cases left a faint, near-linear mark that appeared exactly where voters draw a line to select their candidates.
Arapahoe County Clerk and Recorder Nancy Doty said the marks are so faint that the scanning machine that tabulates the votes does not detect any of them.
"We have tested the ballots, and it doesn't have any effect on the tabulation," Doty said. "I am confident that it has no effect on the voters ballot."
The situation occurs in a tossup county where 104,896 active voters are Democrats, 99,866 are Republican and 100,164 are unaffiliated. It has swung between being Democratic and Republican. And its voters tend to turn out in big numbers.
"This county may be one of the most important counties in the election," said political analyst Floyd Ciruli. "If our nine electoral votes decide the president, this county is going to play a big role.
"To prove that everything is OK, Doty on Tuesday afternoon called both representatives from the Republican and Democratic parties and a representative from the Colorado secretary of state's office to the county's election offices to view for themselves.
County staffers pulled out 100 ballots that had already been returned and had the party officials tabulate the votes by hand. In this purely randomly selected stack of ballots, 61 votes were for President Barack Obama, 37 for Mitt Romney and three for Libertarian Gary Johnson.
Then they ran the ballots through the scanner to show that the faint lines made no difference. The machine accurately counted 99 of the votes. One ballot was kicked out and had to be rerun.
The machine is designed to catch any overvotes on a ballot - instances when someone votes more than once in a one-vote race. When that happens, the machine spits out the ballot for a visual check. The scanner has an 8 percent sensitivity setting, meaning it will catch pencil lines that may have been erased with an ineffective eraser but not much fainter than that.
In the weeks before the ballots were mailed, the county hired a company, Major Scale, to test the system's accuracy by running about 8,000 ballots, Doty said.
Republican county chair Joy Hoffman said she was satisfied after seeing the demonstration.
"It appears to be doing what it is supposed to do," she said.
Deputy Secretary of State Suzanne Staiert also believed that the stickers' imprint didn't cause a problem.
"Having observed the process, we're confident in the integrity and we appreciate Nancy Doty's quick action," she said.
But Democrats were not convinced that there won't be a problem.
"We're concerned," said Martha Tierney, attorney for the Colorado Democratic Party. "We have lots of questions about whether or not this will result in errors in counting. It is not dispositive for me. We'll have to consider some options over the next few days."
Doty said that if people are concerned about a ballot, they can bring them in to the elections office for a new one.
"This has never happened before," Doty said. "A few years ago, people were upset because they didn't get the stickers with the mail-in ballots. We thought it was a nice gesture to put them in. We'll never do it again."