If an FAA inspector noticed the 'strange propellors' and 'grounded it' he would have issued a condition notice, and either handed it to the pilot (if he was around) or afixed it to the airplane.
The pilot (or the aircraft owner) is then responsible to note in the comments section of said condition notice that the aircraft is airworthy (and why) and return this notice to the FAA field office from which the inspector came.
Occasionally, a mechanics signature is required, IF work was needed to bring the aircraft into compliance.
A very straight forward procedure.