There is no consistent, attractive and meaningful symbol for 'no junk mail'. The closest and most elegant is using the Australia Post symbol. The most consistent symbol is actually the colours gold and black, as most No Junk Mail signs are gold and black.
No Circulars is the most old fashioned and bizarre sign.
I start putting advertising in No Junk Mail letterboxes when the signs are starting to get so worn that some words are not fully visible. If you really don't want Junk Mail, at least go to the effort of updating your scabby sign.
I don't really like political No Junk Mail signs. Nor do I like polite ones - 'No Junk Mail - Thank you!' I don't mind really angry ones - 'Warning! If you put any junk mail here we will post it back to you and you'll have to pay the 55c postage!' They're kind of fun.
I don't like letterboxes in the door itself. I don't like having to walk all the way up to your house and then risk trying to shove things through your door while you are trying to open it!
My favourite No Junk Mail signs are these really simple, black and white ones. I don't know who produces them so I can't find an image to show you.
Some really rich, posh, new houses don't have No Junk Mail signs. Is this because these people are so rich that they don't want to stoop to caring about their mail? Or do they like reading junk mail?
I'm not sure what I think about the fancy, posh, gold plaque No Advertising Material signs that are designed to totally blend in as a 'feature'.