When two companies merge, when one of them subsumes its brand into the other, it's only natural that the survivor should advertise its new identity to the world. Except when it isn't.

AT&T (NYSE:T) is one of those cases when it isn't. The company has been around for over a century. I'd argue that, within this nation's borders at least, it's probably one of the best-known brands aside from Coca-Cola and McDonald's. And the fact that the company once known as "Ma Bell," later split into a handful of regional "Baby Bells," has now been bought out by one of its offspring doesn't diminish the fact that everyone already knows precisely who AT&T is.

So why, pray tell, is AT&T -- the reconstituted Ma Bell comprised of the regional phone provider SBC and the long-distance provider AT&T -- embarking on the "biggest ad campaign in its 120-year history?" As far as I can tell, its primary aim is to confuse the heck out of us poor consumers.

I'll explain. Close your eyes. Wash from your mind the fact that I've been talking about AT&T for the last three paragraphs. Just listen for a moment to this slogan and tell me who you think it's advertising for: "Your World. Delivered."

Five gets you 10 that anyone hearing this, and not already knowing who's behind it, would attach that tagline to one of these companies: DHL, FedEx (NYSE:FDX), UPS (NYSE:UPS), or the U.S. Postal Service. This ad campaign gets, hands-down, my Foolish vote for silliest marketing idea of the new year -- and the new year hasn't even started yet.

But it gets worse. If this is truly the biggest ad campaign in AT&T's history (the company's words, not mine), then one can only assume it will be accompanied by the biggest advertising budget in the company's history. Although AT&T is keeping mum on the actual dollar number that amounts to, you can bet it will be a big one. Surely AT&T wants the campaign to boost revenue and reverse the multiyear slide of its sales, margins, and operating cash flow. But ask yourself, which would be more Foolish: to spend huge gobs of cash to (mis)advertise an already well-known brand, or to reduce costs, conserve cash, and drop greater profits to the bottom line?

All of which leaves this Fool sorely confused -- not just over who the tagline belongs to, but over just what the heck AT&T was thinking when it agreed to pay for it.

AT&T is hardly alone in the stupid marketing tricks competition. Once you're done with this column, click on over to revisit GM's (NYSE:GM) Dumbest Move Yet.

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Fool contributor Rich Smith has no position in any of the companies named above.