A proposal that the nation's vehicles be graded on fuel economy evokes Nathaniel Hawthorne's bitter 19-century romance novel, "The Scarlet Letter."

But in this case, the federal government supplies the public scorn, while light trucks — on the rise again in popularity — are poised to bear the mark of shame.

The proposal, one of two developed by the EPA and DOT, suggests window stickers be emblazoned with letter-grades. An MPG rating of 59-116 would earn an A, while 14-15 would merit a C-.

Problem: Every vehicle, regardless of its intended application, would be subject to the same scale. That's like administering SATs K-through-12 and expecting a fair assessment of the student body.

Based on the '10 model-year fleet, a Honda Civic Hybrid sedan would get an A-, the showroom equivalent of a gold star. But a Ford F-150 fullsize pickup with 4-wheel drive would end up with a C, spitting distance from the dunce cap.

No malice intended, according to the federal agencies which signed off on a sticker designed by "an expert panel" of communications pros. "Our interest was in making sure that we were clear," says EPA Assistant Administrator Gina McCarthy.

While the mark reflects only fuel economy, the stigma is undeniable for anyone who has ever suffered the icy stares of schoolyard eggheads.

But there is no "failing grade," McCarthy offers.

Really? As a high-school sophomore, I told my mother there's no shame in a straight-C report card. She didn't buy it.

I wonder how Honda would feel if tow ratings were accorded the same billing as fuel economy and Civic Hybrid stickers got slapped with an enormous D.

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Eric Mayne is a veteran auto industry journalist who has won numerous international awards for news and feature writing.