I seem to recall back in about 2005 the Department of Transport (or whatever their name was), had a big push on securing aircraft. There were fines touted at the time of around $5,000 and there were to be checks taking place at airports, fly-ins and the like. We were all required to fit throttle or prop locks and have a sign fitted that told the potential thief that an aircraft locking device was fitted. If the lock was not visible to someone looking in, you had to fit one of those fabric patches to your aircraft cover, which you could get for free from the government.
This was all heavily promoted at the time.
Is this still in force and is that what you are referring to?