Going down Marshall Drive in Arlington yesterday, a couple of us smiled upon spotting a specialized -- some call it "vanity" -- license tag we'd seen before: I HAPPY

The tedium of such morning trips often is turned around by watching for interesting tags, such as D.C.-issued inaugural tags VA GOP and, on a car that had a dealer license frame from Idaho, BOI C. Presumably somebody already had beaten out that car's owner for the full name of the state capital.

Now comes word from Richmond that the Virginia Division of Motor Vehicles is issuing annual prizes, in the form of certificates, for the most timely and original of the Old Dominion's specialized plates -- or, as the agency calls them, CommuniPlates. And the envelope, please -- ta, TA! -- the winner for 1984 is: B4IM30

That, of course, pronounces out to "Before I'm 30," whatever that implies -- marriage? job? or ownership of a Mercedes? Rounding out the top 10 plates for 1984, according to Motor Vehicles Commissioner Donald E. Williams, were:

YBUY4N (Why buy foreign?), VAMADE (Virginia-made), LUVAPC (Love a personal computer), VIDEOU (Video you), WKENDR (Weekender), 2BA (Tuba), WEVOTE (We vote), IOONIT (I owe on it) and BREAKN, the last of which we'll let you figure out.

None of the license holders' names was announced by the motor vehicles agency.

By the end of 1984, commissioner Williams said, there were 322,157 valid CommuniPlates -- one out of every 11 cars in the state -- compared with 271,200 in 1983. The $10 extra cost for such a plate produced more than $3 million that went toward highway maintenance.

Motorists requesting such tags in Virginia may request two to six numbers and/or letters and spaces for standard automobiles or motorcycles (second and third choices invited). And, please, keep it clean, or the state will have to do it for you.