What are the rules for using the dented helmet logo for a shirt or something that you plan to make only one of and plan on keeping yourself?
As a newspaper editor and a photographer, I find someone being considerate of copyright issues to be quite refreshing. Unfortunately, I can't answer this question specifically, but I'm sure someone will chime in. I'd guess that if you were making the shirt for yourself and not using the image for commercial gain that it shouldn't be a problem, but it's not my place to say. Good on you for asking though
Looking at the logo documentation. Does the shirt run happen two times a year?