This 'letterbox notice' has been invented by someone (not me!) who has looked into whether or not it's possible to charge junk mailers for ignoring anti-junk mail notices. The sign appears to deter junk mailers all right but – before you get all excited – there's no way to actually enforce the notice.
For the enforcement side of things the person approached a couple of parking enforcement companies. The notices are fairly similar to 'no parking' notices on private land, and the companies were enthusiastic at first. After studying the finer details of the proposed scheme, however, they said it couldn't be done – or at least not for £60 per item.
The main 'challenge' was that the enforcement company would, for legal reasons, have to send an invoice to the deliverer rather than the sender or distribution company. This is impracticable. Unaddressed junk mail very rarely includes information about who delivered it, which means the enforcement company would first need to contact to the sender (i.e. advertiser) to find out which company was responsible for the delivery and then contact the distributor to find out the name and address of the deliverer. Neither the sender nor distributor are likely to be co-operative.
Even if that hurdle could be taken a next problem would be people challenging the fine (strictly speaking it would be a 'junk mail handling fee' rather than a 'fine' but no recipient would care about such nuances). And they would probably be successful. As a deliverer I could easily say that no notice was displayed at the time of the delivery – it would be up to the householder to prove that the sign was there. Or, I could claim that the item was delivered by a child who happened to be playing Postman Pat and asked if he could deliver the junk mail for me. If you've ever visited forums about how to fight fines for parking on private land you can no doubt think of other ways to avoid paying.
And even if the deliverer could be found and forced to pay the 'handling fee' the issue would probably not end there. The deliverer might be very tempted take revenge. And rightly so! Delivering junk mail is a shit job which pays very little money. £60 might not be much for an enforcement company, it's probably more than a junk mail deliverer gets for a hard day's work. It might be worth noting that the scheme wouldn't have earned householders a single penny – but any retaliation would almost certainly be aimed at them.
One strike, you're out
And that's where we get to the ethics of the scheme. Its major flaw is that it would be run for profit by an enforcement agency. The profit motive rules out the possibility of making the scheme humane. I strongly feel that the scheme should adopt, at the very minimum, a two strikes you're out policy – that is, after ignoring the sign for the first time you'd only get a warning. Such a 'soft' approach isn't profitable, and so the scheme would have been one strike you're out. The scheme wouldn't have been able to account for genuine errors – inconsiderate and considerate junk mail deliverers would be chased for money alike.
To cut a long story short, I wasn't comfortable with the scheme. We do have a problem in the UK with 'No Junk Mail' signs being ignored but lining the pockets of enforcement companies to hunt down junk mail deliverers isn't the solution. The problem is with the senders, who are refusing to formally recognise letterbox signs – they're the root cause, and they're the ones we should go after. I'm quite happy that the scheme turned out to be unviable.
Life after the junk mail handling fee
All that said, the letterbox notice itself appears to deter junk mailers. I'm not going to produce the signs as there's no way the junk mail handling fee could (and should) be enforced. However, you're free to roll your own! If you want to do something with the sign you can download it as a tarball. Inside you'll find the sign as a PDF and PNG, as well as two Scribus files (one with texts outlined, the other with the 'proper' font). I've licensed the sign under the WTFPL, which means you can do with the artwork what you please.
And if you're really interested in taking legal action against junk mail senders you might want to think about combining the letterbox notice with this trespass notice. The combo wouldn't quite solve the (legal) problems with the trespass notice but it could strengthen it. Who knows, there might just be a way to stop junk mailers with some sort of legal notice…