Bigger doesn't necessarily mean better. But more often than not, having the opportunity to get very big in the retailing sector means you did enough things right to get lots of customers coming through your doors. And while most Americans may not recognize Signet Group (NYSE:SIG), I believe most of us are pretty familiar with their core U.S. jewelry stores, Kay Jewelers and Jared.

Fourth-quarter results, as well as full-year results, are something of a tale of two countries. Times have been challenging in the U.K., with total sales down about 8%, same-store sales down about 8.6%, and operating profits down about 20% in the fourth quarter. In contrast, U.S. sales were up 23%, same-store sales were up 6.4%, and operating profits climbed 16.8%.

So while the company is hunkering down and trying to eke past this rough patch in the U.K., the U.S. business is clearly growing very well. In the fourth quarter, Signet's U.S. operations did a fair bit better than any of the other major U.S. jewelry specialists -- better than Zale (NYSE:ZLC), better than Tiffany (NYSE:TIF), and better even than the much-beloved Blue Nile (NASDAQ:NILE). In fact, this boring old bricks-and-mortar retailer (isn't that so 1980s?) is now the leading specialty jewelry retailer in the country, though probably still behind Wal-Mart (NYSE:WMT) in terms of total jewelry sold.

The good news/bad news is that Signet is in no way stepping off the gas pedal. In fact, the company plans to spend at least $1 billion over the next five years in the U.S. for store expansion. While it's certainly reasonable to expand upon a winning formula, that's a billion dollars that's going to be tied into capital expenditures and working capital. Of course, with so many of Signet's store-based competitors in the U.S. foundering, this could be a great opportunity to grab them by the throats and make that moat all the deeper and wider.

Signet trades enough so that an average investor can build a position without too much trouble, but anyone considering this stock has to stay cognizant of the risks of a somewhat illiquid stock. Of course, when you're talking about the world's largest jewelry retailer, the leader in U.S. market share, and a company with respectable returns on capital to boot, maybe a little risk isn't too much to swallow.

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).