Stan Allen of Northwest was studying the back of a $10 bill one day when his curiosity bell gonged.

"I cannot resist a cry for help in identifying the make, model and year of the little sedan tootling along" in the picture on the ten-spot, Stan writes.

"Is it a Chevy? A Dort? A Hupmobile?

"It certainly isn't Superman. But what?"

Answer: It's an Approximation.

Once again, the ever-cautious government plays it close to the vest.

"A careful examination of the vignette on the reverse of the $10 note will show that four automobiles are included in the design," said Betty L. Russell, public affairs supervisor at the Bureau of Engraving and Printing.

"While the cars are similar in appearance to those manufactured in the 1920s, none represent a specific make or model of a particular company. This was done in keeping with the established policy that no feature depicted on currency should be identifiable with the product of a particular manufacturer, thus avoiding a claim of preferential treatment."

What about the American Security Bank branch that sits right behind the four cars, and whose presence "right on the money" is the guts of an extensive ad campaign?

The building is not identified as an ASB branch on the $10 bill, notes bank spokesman Ted Stark. Besides, "we sought permission from the Treasury Department to use it as we use it in the ads." Permission was granted, as long as the ads didn't use or depict actual bills, which they don't.