This is great use of law. I can think of a number of other situations where being able to ask for a card would provide excellent protection and accountability. This quote is from AlterNet: Rights and Liberties: Catch and Release:

Mike Walker recently got bumped by the cops – again. This time it went down on a Friday afternoon as he was heading home from school with his boy Brandon. The eighteen-year-old northeast Denver natives were treading steady down tree-lined 29th Avenue toward Williams Street when a District 2 Gang Unit police cruiser lurched across the intersection and onto the sidewalk in front of them. Two officers got out and told them they matched the description of a suspect in a ring of car thefts. "He said that the guy looked just like us," Walker recounts. "A big black man."

A quick ID check proved that neither Walker nor his friend was their guy, but Walker says that Officer Rick Eberharter then accused him of representing the Tre-Tre Crips simply because he was wearing a blue hat, blue shirt and dark-blue jeans. (Actually, Walker is the son of Pan African Arts Society director Ashara Ekundayo and has been a local community activist since the age of fourteen.)

Walker said, "No way," and quickly asked the officers if he and Brandon were being detained. Eberharter answered in the affirmative, and then, Walker says, he and his friend were handcuffed, searched, questioned, checked for outstanding warrants, verbally abused and finally cleared of all wrongdoing and released. "Have a nice day," Walker remembers the officers saying as he stuffed rooted-out pencils and binders back into his bag. But before the police peeled off, Walker made sure he did one thing: He demanded their business cards.

Since 2001, every police officer in Colorado has been obligated to offer a business card if they detain someone in a traffic stop but don't cite or arrest them. This was established as part of House Bill 1114, which was passed a year after Governor Bill Owens's 2000 executive order banning racial profiling. The ban was issued in response to a series of nationwide studies that found that law-enforcement agencies were specifically targeting Black and Hispanic motorists for vehicle searches ("Target Practice," January 24, 2001). The bill not only required that business cards be given out, but mandated that all law-enforcement agencies have a written policy against racial profiling and provide officer training on the issue.