I found this outdated article from 2017 that claims that:
The easiest way to deal with mail from former tenants with no forwarding address is to write “Return to Sender,” “No Longer At This Address” or “Moved” on the outside of each envelope.
Of course, the easiest way to deal with such mail is not to do free work for the Direct Mail Marketers and Postal Service. The easiest way is to get the Postmaster to do their job!
According to a 2020 document from the United States Postal Service (USPS) detailing how to refuse unwanted mail and remove name from mailing lists:
An addressee may request the postmaster, in writing, to withhold from delivery (for a period not to exceed 2 years) any foreign letter or publication material with a specified name or address on the outside.
So there you have it. Instead of wasting your time writing “Not at this address” on everything (the only legal course of action once delivered to you) you can get delivery blocked (but only for 2 years at a time – as if the person might come back?) and stop the flow at the source!