It's tough to be a cartoonist lampooning Wall Street today.

They keep changing the visual cliches on you."Fat cat" and "bloated capitalist" don't really work when it comes to such current targets as Frank Lorenzo and Michael Milken, who look more like poster boys for Jack LaLanne. The old ticker-tape machine has been gone longer than Lindbergh. And when the stock market crashed Oct. 19, 1987, not a soul plummeted in panic through the canyons of Wall Street; the windows in the new office buildings are sealed shut.

Then there's the ornately engraved stock or bond certificate, a relic that is perennially endangered but has so far survived for a most excellent reason: despite decades of soothing words from those who want to eliminate it, millions of average investors just plain don't trust the computers.

Anyone who has ever done futile battle against some mindless, incorrect but seemingly ineradicable monthly billing will sympathize with those who insist on being able to hold their certificates in their hot little hands - or at least their hot little safe-deposit boxes.

History, though, is working against these traditionalists, too. More and more investors are finding it convenient to leave their holdings with their brokers, which as a practical matter means relying on monthly computer printouts. And in some areas, notably debt securities such as bonds, investors increasingly may have no choice. The frame-worthy certificates that bond purchasers have been receiving for more than 200 years may soon go the way of high-buttoned shoes, the buggy whip and five-cent cigars.

While stock investors can still usually get a certificate if they want it, bond investors often don't have the option. There's an unmistakable trend toward replacing physical certificates with a computerized record of bond transactions, forcing the investor to rely solely on the blip of a computer memory and a broker's confirmation slip to prove ownership.

In recent years this approach, called "book entry only," has gained momentum rapidly as issuers have sought to reduce their costs by eliminating certificates for new bonds. Some individual investors may grumble, but financial institutions tend to love it, focusing on the convenience and economy of computerized records. And it means big business for companies like Depository Trust, the largest of several firms specializing in computerized security-processing systems.

What many see as the eventual death knell for stock and bond certificates of all kinds first sounded with federal legislation in 1973, authorizing depository systems for institutions but specifying that individual investors could continue to request certificates. "Book entry only" deals, limiting investors to a "beneficial" interest in securities they never actually see, began to emerge just four years ago, but they have spread like a computer virus, accounting for 35 percent of all municipal bonds sold in 1988. Muni specialists think the portion may reach close to 50 percent this year.

Many individual investors in municipal bonds are less than enthralled. A survey conducted by the Market Facts research firm found that 83 percent of muni owners favored maintaining the traditional system of getting and storing physical certificates, either themselves or with their brokers. In addition to concerns about computer security and accuracy, there are complaints about new maintenance fees and other charges instituted to cover the costs of "book entry only."

So far, though, the issuers and institutions seem to be winning. Nor is the trend restricted to municipal bonds; in 1987 IBM Credit Corporation distributed the first "book entry only" security to be listed on the New York Stock Exchange, and other uses range through the modern debt spectrum, from convertible money-market preferred stocks to mortgage-backed securities and warrants.

One business that is obviously unenthusiastic about this trend is the printers that produce the traditional engraved certificates. But Stanley Kreitman, president of the biggest firm in the field, United States Bank-note, told me his opposition was limited to the lack of choice for individuals. "Those who wish to receive certificates for their securities should be entitled to exercise that option," he said, adding that certificates remain "the only negotiable, documentary evidence of proprietary ownership."