I used to add "Embellish" to "Remarks" section of the ICAO flight plan when I was charter flying, off airways - expecially over East Anglia (UK). PA31 - Chieftain.
It was an automatic signal to ATC that I was open for interception and I was usually handed over to London Mil for my radar service.
It proffered me a great service from ATC and a fantastic air display for the passengers - who were kept informed over the PA. They loved it.