U.S. trademark registration 4,473,631 was issued to one Paul Ingrisano, aka "Pi Productions Corp" of New York. In January, the U.S. Patent and Trademark Office gave Ingrisano a trademark on the symbol π. pi followed by a period: a design Ingrisano uses on T-shirts sold at some brick-and-mortar stores.
When Ingrisano discovered that California-based print-on-demand outlet Zazzle offered an array of clothing items that featured the symbol pi, he had his attorney send the company a strongly-worded cease-and-desist letter this month demanding their removal.
"This would be like McDonalds claiming the letter M as a trademark," wrote Jez Kemp, whose Zazzle store offers apparel imagining pi dressed in a pirate costume. "The trademark is in the combination of style and symbol, not the symbol itself."
Attorney Millet defends the cease-and-desist letter. He says that to his knowledge none of the designs sold through Zazzle included the exact trademark π. -- pi followed by a period -- but some of them were confusingly similar to his client's design.
In 2011, Ingrisano attempted to trademark "I<3" artnet reports, which was "published for opposition" in June 2013. Reebok's intellectual property watchdogs claimed in a December 14, 2013 "Notice of Opposition" that "I<3" is too close to comfort to its own "I3" trademark.