There was one guy that received a letter from the FCC that listed four violations. The last one was for using a non-type certified radio. That is not the reason he was investigated. They showed up because he was jamming a repeater. While they were there, they noticed he did it with a non-type certified radio and just threw that in for good measure.
To my knowledge, that is the only time it has ever shown up on a letter and, like I said, that was not why they showed up at his house.