Simple Way to End Voter Fraud - Purple Fingers

From the Campaign Stop, National Review Online, a simple solution to the problem of voter fraud, such as ACORN's widely reported fraud across twelve states:

"Picking up from a thought by Mark Steyn, why do Iraq and Afghanistan have better protections against voter fraud and multiple voting than the United States? Why does the simple, visible, tough-to-evade purple finger ink get put into effect in new democracies in those countries, but we can't get something so simple and effective on the books here in this democracy?"

"What would it take to get 'purple finge'" rules here in the United States?"