I assume The Villan is not in the USA since we don't use the word "postie" here.

For the benefit of any Americans who might this thread, I will tell what I know about American postal procedures.

If you mark something "Return to Sender" it probably won't accomplish what you want.

Regardless of what you write on a letter or package, it won't necessarily be returned; that depends on what level of service the sender has paid for, or promised to pay for. Generally, First-Class mail and packages can be returned, while advertising mail can only be trashed, unless it was endorsed by the sender with special instructions such as RETURN SERVICE REQUESTED.

Unless the sender has specifically asked you to do so, I wouldn't recommend using business-reply envelopes to notify the sender that you don't want their mail. Often the job of opening and processing business-reply mail is outsourced to a fulfillment company. These companies are paid PER PIECE to FILL ORDERS—hence the name. They employ low-paid, low-status, low-skilled, overworked employees to process their customers' orders. These people have no sense of loyalty to the company that is sending the mail, and no incentive to do anything that is outside the terms of their contract (the company) or outside their job descriptions (the employees). Any complaints, non-routine requests, or miscellaneous correspondence that they receive will probably be "lost." Receiving bricks or candy wrappers in the mail is definitely not routine. Can you imagine a low-level employee forwarding a brick through interoffice mail to the person who actually has control of the mailing list? They'd probably fire HIM.

Finally, if you are getting unsolicited mail from a company you have never done business with, it is because the company has bought a mailing list, probably for one-time use only, from a list vendor. (Of course the same company might buy the same list again later, thus giving you the impression they have you on their own permanent list, but this is probably false.) Therefore the sender CAN'T remove you from the original list because they don't own the list. You won't be added to the sender's own permanent database unless you order something. If you write to them demanding that your name be "removed", they could, theoretically, forward your request to the list vendor, but they have practically zero incentive to do so.

The best way to reduce your unwanted mail is to do exactly as leeneia advises above.