(CNN) Bryan MacCormack says he knew what to do when ICE officers pulled him over with paperwork in hand: Read the fine print.

MacCormack says he was driving two undocumented immigrants who'd just had a court hearing in Hudson, New York, when the officers stopped his car. They showed him a document through the driver's window.

The ICE officers called it a warrant. MacCormack told the officers something was missing: a judge's signature.

A video showing part of the March 5 verbal standoff was widely shared on social media this week. And advocates are pointing to the exchange as an example of how "know your rights" lessons, which immigrant rights groups have been teaching across the country, are working.

'Those are not warrants'

Read More