I think it was a money saving tip on this site that said "put a no junk mail sticker on your mailbox" that way you stop getting all the brochures advertising lots of things you don't need but it makes you want them, it was somewhere in here: Money Saving Tips now ACCC have released a Free Do Not Knock Sticker which will be very hand as well:

Door to door - do not knock sticker | ACCC

The ACCC has produced this sticker to help you avoid unwanted door to door selling.

If you can't wait for the sitcker they also offer a free printable PDF: Do not knock which you can print out and stick on your front door yourself.