[JumpCrisscross]

> increases likelihood of it getting someone's attention

Huh, I’d toss it as spam. Addressing to legal seems more likely to deliver without side effects.

> Registered mail, return receipt, provides legal proof of delivery

These are better.

[dredmorbius]

A hand-addressed letter with that labeling tends not to be instantly discarded as spam.

Routing mail within large organisations is its own complex problem. What "demand letter" indicates is where the letter should go, and to whose attention it should be brought.

Any organisation of even a fraction the size of Amazon, Inc., will have staff whose job it is to assess the credibility of such claims. Your heuristic is unlikely to be followed by them, and would present significant risks if widely practiced. Courts and juries in particular tend to frown on ignoring such communications.