Humorous notices of the "You don't have to be mad to work here" type are an institution. Visit shops, offices, pubs and restaurants across the country and you'll find them nestling among the other notices on the wall or pinned to a computer or till. While these are often crude, handwritten copies of signs someone has seen or photocopies of an original, the only explanation for the spread of such witticisms is that they satisfy some kind of need in the worker's psyche.
Some workplaces make a point of humour. Soho hang-out The Dive Bar is covered in such placards. Some of the reminders to staff read: "Tell me again how lucky I am to work here, I keep forgetting"; "Stupid mistakes are always made by others, we only make unavoidable errors"; and "In case of atomic attack, keep calm, don't panic, run like hell and pay your bill".
Bar manager Mike Cowell says the wife of the boss has been adding slogans to the bar for many years. "She's been collecting them since the early Eighties," he says. And does she really find them funny, or is this some kind of kitsch statement? Mr Cowell says it's not meant to be kitsch: "She finds these things genuinely funny, not naff."
While The Dive Bar may have turned into something of a shrine to this kind of humour, the most common place you'll find the humorous poster or placard lurking is in the reception areas, typing pools and kitchens of offices across Britain. There, they exist to brighten up the dull moments, even when the joke has long since ceased to be funny.
So who makes these things, and are they still in mass production? Lindsey Parsons, at Southampton-based giftware manufacturers Russberry, remembers that when the company started up in the Sixties, humorous placards were all the rage. But she says they haven't included them in the range for many years: these days, it seems, office humour has grown up - in Britain, at least. "There's just not the demand for that sort of thing any more: it's too American for the British sense of humour," she claims.
Ms Parsons does appear to have a point. Some would argue that British humour is renowned for cruelty and insight, and for the unique flavour of its dark comedy. According to this line of thinking, the only place a "You don't have to be mad to work here but it helps!" notice would summon a laugh would be hanging in the offices of an organisation such as MIND, which employs some staff who have suffered from mental illness.
But in most other locations, these notices are considered old-fashioned and jokey. Office humour functions in the same way as the material of a comedian like Brian Conley; it's more of a comfort valve than a proactive attempt to induce mirth, but it nevertheless still finds a place in some people's hearts.
The easy accessibility of the office photocopier probably explains why once one office humour poster has got into the office, it can spread throughout, bored staff pasting legends into every corner, such as "Our boss is always right; misinformed perhaps, sloppy, crude, bullheaded, bad-tempered, fickle and even stupid but never wrong!" and "Rule No.1: The boss is always right. Rule No.2: If the boss is wrong see No.1".
Oddly enough, while these digs at the boss might be considered risque, it's often the boss who introduces the office humour into the workplace first. Could this attempt at giving the staff packaged and controlled weapons of protest be aimed at stopping them from actually talking back or complaining? This is the theory of Ben Spieman, the ad sales manager on a London legal magazine, who recently grew so weary of his boss's ardour for collecting and pinning up office humour posters that he led an insurrection by encouraging fellow workers to illustrate "You don't have to be mad to work here, but it helps" placards with their own interpretations of madness. "Office humour is just a purchasable dissent; an accepted outlet for dissatisfaction. It's as oppressive a part of the office as fluorescent lighting," Spieman explains.
It is a well-known truism that the British find it difficult to complain. Perhaps office humour's success is down to the way it provides a means of articulating our resentment at work but in a non-confrontational and ultimately ineffective manner. Brits are often happier to make jokes in the "mustn't grumble" vein than they are to confront their superiors and voice dissatisfaction. Office humour is like the modern-day blitz spirit - meant to keep you smiling through, no matter what the problem is.
And that's why office humour is here to stay. In the days where almost everyone has access to photocopiers, faxes and now e-mail, office humour has taken on a life of its own. It may not be purchased in the quantity it once was, but it will exist and multiply as long as there is a bored, mischievous little devil in every office.