Dark, stark subway tunnels -- the abyss we commuters stare into while thinking profound thoughts, or at least shallow thoughts that seem profound at the time -- may soon be an obsolete pleasure. An innovative advertising firm called Submedia has been offering mass transit systems around the country a fairly simple technology that turns their dingy tunnel walls into plush revenue centers. A series of metal boxes, installed side by side on a tunnel wall, contain backlit compressed images; when a train speeds past, the images appear to the passengers inside the train to move, like a child's flip book. Trials are already underway in selected tunnels beneath Atlanta and New York, with more to come. Ten days ago, Washington's Metrorail -- a public transportation venue long proud of its largely schlock-free atmosphere -- became the latest system to approve tunnel advertising.

The significance of this new advertising forum will doubtless be misconstrued. You'll surely hear critics whining about how yet another line has been crossed, another sacrosanctuary destroyed. Is no place safe? ATM screens now hawk merchandise. So do elevators. TV monitors over the urinals at ESPN SportsZone busily brand the network while we relieve ourselves. If not for a brief spasm of alleged high-mindedness three weeks ago, the bases in major league baseball stadiums were to be tattooed with Spider-Man's likeness, to promote the upcoming movie sequel.

My problem with all this is different: I think we're not being nearly creative enough.

As imaginative as the above ideas are, they're still bush league. It's criminal to think how much primo experiential real estate is not being used to capture the hearts and wallets of the American Consumer. A few suggestions for new ad space to tap:

* Clouds. Think about it: a bunch of powerful klieg lights and a projected image of a Chevy truck . . . especially if the clouds are the puffy cumulus kind, shot through with late-afternoon sunlight. How transcendent would that be? Who says the skies belong to the birds, or nature itself, or God, or all of us?

* Dreams. All that university time and money devoted to sleep research and we can't infiltrate dreams with product placements? The beauty part is that it benefits the dreamer at least as much as the advertiser. How much less angst-ridden would you be if that recurring nightmare about teeth falling out climaxed with you standing outside a CVS stocked with Crest toothpaste? How much more comforting would it be if Oscar Mayer and Dunkin' Donuts sponsored the one about the hot dogs chasing the donuts through the tunnel?

* Soles of shoes. We look at thousands of them every day -- when strangers cross legs on the bus, at work, in group therapy. Are they not empty billboards yelling to be scrawled on? Paul Simon sang about the girl with "diamonds on the soles of her shoes." De Beers?

* That instant after we stop inhaling and right before we start exhaling. A microchip in the nose releases the faintest nuance of a fragrance, from Chanel or Estee Lauder. After all, you weren't really using that tiny moment to smell something else, were you? The atavistic, Proustian power of the olfactory sense does its magic, so the next time you walk through a department store and pick up the scent during your usual inhaling, you just have to buy it.

* Symphonic "rests." A long time ago, composers such as Beethoven and Mozart overused the "rest" symbol to indicate a short break between one musical phrase and the next. Whatever. I have to assume they had their reasons. But just because 100 members of your local Philharmonic are occupationally obligated to take these two- to five-second hiatuses doesn't mean that the audience can't be treated to a crisply delivered pitch for Cingular's Nation FamilyTalk Plans package. Or that the fluegelhorn player, who's underworked anyway, can't quickly paraphrase a Pepsi jingle.

Then you go back to the Requiem. What is the problem?

* Preschool nap time. Speaking of "rest" -- there's at least 45 minutes where my son and his schoolmates, post-juice and snacks, just lie around on blankets, doing nothing. So some of them fall asleep. Most don't. Wouldn't this be a sweet time for them to hear, from some soothing CD, a lullaby about the latest American Girl or Bionicle? Are we barbarians to deny them this pleasure?

* Internal organs. Surgical tattooing is a safe, time-tested method of display -- so why not a Nike swoosh on your kidney? Golden arches on your duodenum? Granted, there's a downside: No one, not even you, can see the advertising, at least while you're alive. The upside? If you donate your body to medical science, or if you're selected for an autopsy because of troubling circumstances surrounding your death, you'll leave a lasting impression on forensic scientists and especially medical students, a highly desirable demographic. Wouldn't it be wonderful, too, to know that dead people can still move product?

Author's e-mail: andyp@onebox.com

Andrew Postman, a writer in New York City, is willing to emblazon the windows of his home with holograms of Kraft cheese products, for a price.