As of December 28, 2015, no live official trademarks were found on USPTO.gov for the exact terms/numbers
In addition, BJ = Beijing, which has a population of 21,000,000+.
As ordinary 10, 11, and 12-number domains, this letter-number configuration may mean little to average Occidentals (other than as an easy-to-remember cool pattern); heck, we don't fully understand the premise, either...
Disclosure: In Chinese culture, "4" is generally considered an unlucky number because it sounds like "death."
A Western comparison: the number 13, also a harbinger of death, is considered to be an unlucky number, but, at least once a year, Westerners celebrate unlucky 13 by dressing up as ghosts, skeletons, and other scary creatures, such as Justin Bieber and Miley Cyrus.
However, in this case, the "4" is necessary to the consecutive string of numbers.
Indeed, according to the website Travel China Guide, in China’s long history, the number 4 has been widely used and accepted as a number to represent common patterns in nature, architecture, literature, important inventions of ancient and modern China, and more.
Click and scroll to "Wide Use of No. 4" for some positive examples.
But we'll have to allow potential buyers to arrive at their own conclusions.
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