From the article:

Lawyers for product manufacturers now fear clients are liable for up to $500 for every tube of mascara or box of garbage bags marked with an expired patent--an error that turns out to be quite common.

In recent months, would-be plaintiffs have been fanning out across retail stores and the Internet searching for expired patent numbers on everything from toothpaste to toilet plungers.

Now that's classy. Of course the reasoning?

The people behind the suits say they see themselves as consumer advocates, helping to protect legitimate inventors from giant corporations who are pretending to have patents to keep competitors from stepping on their turf.

"It chills competition, it misleads the public and takes away from the credit patent holders deserve," says Daniel Ravicher, founder and executive director of New York nonprofit Public Patent Foundation, which has filed numerous suits.

Consumer advocates? Chills competition?

Let me give some insight: Joe Public isn't going to care about a patent. It means essentially nothing to them. The only people that would care about it are entities looking to produce an identical or similar product. At that point in time, all the said entity has to do is do a quick search to see if the patent is expired or not. You can even type a patent number into google and it will pull it up.