The anonymous tipping of the police? Sorry, but this really sounds like something made up by loyals trying to make the watchtower look better. I cannot think of one valid reason why the society would need to be doing this anonymously, especially if it is the law.
I only mention anecdotal as I did not have first hand experience. I have had two elders (one was my father) relate experiences they have dealt with where they were advised they could report. This was in the case of minors at risk. There is no doubt this circumstance is rare and I am certainly not suggesting that there is any proactive response by the organisation when the question of the moral and ethical responsibilities of the elders is raised - the precisely opposite situation is the case in the 99% of cases, as shown by the first hand experiences on this thread.
There are specific instructions to report anonymously as evidenced by the internal Bethel memo posted as part of the ARC submissions. This only applies in the case where mandatory reporting is concerned.
The anonymous aspect of the reporting is typical Bethel legal nonsense designed to protect the organisation from being dragged into the matter in any manner.