Phil Michaelson embraced a new tactic in trademark battles—online shame—after he created a web cookbook last year for people to collect and share recipes.

The cookbook let consumers save the instructions for making a certain dish by clicking on a "K" for "Keep." But AdKeeper Inc., a New York-based service that allows users to save, or "keep," online ads, sent Mr. Michaelson a letter claiming his use of the "K" and "Keep" as well as his website's name, KeepRecipes.com, constituted "blatant trademark infringement."

Mr....