I found out the Interstate shield design is a registered trademark not AASHTO. Have they ever sued anyone over that?
I've always been curious given how many people technically violate the trademark when they produce things like Interstate stickers and novelty shields.
Trademark law actually requires the trademark holder to defend the trademark. Given how long the interstate shield has been around and there being no known lawsuits, it's actually very likely any actual defense going forward would lose in court for this reason.
According to the FWHA...
"On September 19, 1967, the U.S. Patent and Trademark Office issued Trademark Registration 835,635 for the shield. According to the American Association of State Highway and Transportation Officials, the trademark "has been used several times over the years to prevent or remove Interstate-like signs near the Interstate highways, where they might confuse the traveling public and cause accidents."
So my guess is they don't care about novelty stickers and the like, but do care if they violate putting signs up along the highway. Which makes sense.