I saw something in a record store the other day that I have never seen before - a poster of a rock 'n' roll band with all the members smiling pleasantly and looking like normal people.

That violates all the international rock 'n' roll conventions on posters and album covers. Somewhere it is written that the only proper way to have your picture taken if you are a member of a rock 'n' roll band is to stare, unsmiling, into the camera with an intense, angry look.

But why? Rock music is fun. Why do its musicians feel compelled to portray themselves as so terribly serious? To look at those posters and album covers, you would think they were classical musicians who had just recorded "Hooked on Funeral Dirges."

As a matter of fact, some of the most somber classical music albums are produced with a picture of the musicians standing there in their tuxes with big, happy smiles on their faces. Everybody in the music world is backward. But those rock musicians aren't in tuxes or even in simple blue suits. They are in their regulation social rebel gear and that tells us something. Our choice of clothes and our poses in photographs represent the way we want to be perceived by others. Rock musicians want to be known as bad. Rock music is deeply rooted in the counter-culture. It's heroes are anti-heroes, intent on offending fogies.

And so if you want to be a rock hero, you start with the costume. Then, if you get around to it, you take music lessons.

Writing is like that. An individual will decide one day that he wants to write the great American novel. He notices that a lot of novelists are bearded guys. So he grows a beard. And then he buys a typewriter and some pencils. And then, if he gets around to it, he studies literature and writing. And some day, after the beard has grown, he may even sit down and start trying to write.

That's backward and it stems from a fundamental misunderstanding of writers. Novelists have beards because they are so obsessed and preoccupied with their writing that they forget to shave and bathe. They work so hard that they stink but their writing doesn't.

Growing a beard first, if you decide to be a writer, is like deciding you want to be an auto mechanic and beginning, not by learning about engines, but by smearing grease on your body.

Grease on auto mechanics, beards on writers and careless clothes on the kind of unstructured person who makes original music are all a consequence not a cause. Beards don't cause books to be written. Book writing causes baths and shaving to be missed, which causes beards to be grown.

Similarly, wearing irregular clothes doesn't make you a musician. Being a workaholic musician causes you to pay little attention to clothes.

And of course, rock musicians, auto mechanics and novelists all share another factor: Their jobs don't have the strict dress codes of lawyers and bankers and insurance salesmen. They are not in suit-and-tie jobs.

On the other hand, rock music does have some clothing rules. You can wear anything you please, so long as it isn't a suit and tie. You show up at a rock concert with business clothes on and they'll hoot you off the stage. There is a strict dress code in the rock music world against suits and ties. Hence, the studied informality of wild hair and wilder costumes. Those are the official suit and tie of the rock musician.

And you must never smile. Boy Scouts smile. Sunday school kids smile. Boring, unoriginal, puritanical twits smile.

Bad boys never smile. Bad boys are grim and angry. If you point a camera at them, they stand sideways with their arms folded over their chests, glaring cynically into the lens in a pose that lets all the world know they are real bad dudes.

I don't know which is funnier 18-year-old musicians doing that, trying to look as worldly as their music or old duffers in the Rolling Stones, pushing 50, wearing the same kid costumes and still trying to look teen-age intense for the camera. (Mick Jagger should stop wearing sleeveless T-shirts now that his shoulders have wrinkled.)

I may write a novel about it. But first, I want to grow my beard a little longer.