Gary Locke, the U.S. ambassador to China, has been a trending topic on Sina Weibo, China’s Twitter, which has 300 million registered users. Among other things, Sina Weibo’s netizens have chattered about Locke’s salary and his habit of carrying his own backpack.

Locke isn’t himself active on Sina Weibo (weibo means, literally, microblog. We would pronounce it as something like ‘way-bou’).  More than a dozen other American politicians are, reportsChina Daily. Dave Heineman, governor of Nebraska, posted his first message “Hi, China!” on May 10th. The Chinese press said that a number of Chinese users greeted him, saying “Hi, Dave, welcome to China.” Fellow Nebraskan Jim Suttle, mayor of Omaha, is also on Sina Weibo, and posted his first message in Chinese. Three minutes later, his second Chinese message welcomed Chinese people to work, invest, study and live in Omaha. Chinese Weibo members responded enthusiastically with questions relating to visas, tourism and study.

The first U.S. politician on Sina Weibo was Daniel Wong, a former mayor and city council member of Cerritos, California who moved to the U.S. from his native Hong Kong as a youth. He’s known as Huang Jinbo on Sina Weibo.  He opened his account in August 2009 and now has more than 20,000 followers.The most popular U.S. politician on Sina Weibo hasn’t actually held political office — it’s Neil Bush, brother of former U.S. President George W. Bush. Bush, a businessman, has 120,959 followers at present (as compared to only 153 followers on Twitter). Edwin M. Lee, the mayor of San Francisco, posted regularly on Sina Weibo, though in English, during his campaign for mayor.

U.S. politicians are not the only ones adopting Weibo accounts. According to a Sina Weibo spokeswoman quoted on Xinhua.net, about 300 foreign officials and representatives from international organizations have opened Weibo accounts. Christine Lagarde, managing director of the International Monetary Fund, has 760,000 Weibo followers, versus 52,000 followers on Twitter. One follower, “Xiao Sha Jiang Fu” said “This is the closest communication between IMF Managing Director and me.”

The blog TeaLeaf Nation noted that a number of foreign politicians message regularly on Sina Weibo. Boris Johnson, the Mayor of London, used his Weibo account to encourage the Chinese community in London to vote for him. Others post personal messages discussing their thoughts on food, family and travel.

According to a Xinhua report from late Friday evening, a spokesman from China’s National Internet Information Office has announced that several internet companies, including Sina(NASDAQ:SINA) and Tencent (HKG:700) , have been legally punished for permitting the spread of unfounded rumors. Specifically, the report cites unfounded rumors that were spreading like wildfire on Sina Weibo of an attempted coup d’etat happening in Beijing.

It’s not clear exactly how the companies were punished — the report just says that they were “seriously criticized and punished accordingly” — but the language is quite strong. The rumors are referred to as exerting an “evil influence” on society, and those who spread them are called “lawbreakers” who acted “maliciously” and “without reason.” Xinhua is China’s official state wire service, and these words were probably carefully chosen.

The report ends with this sentence: “The two companies [Sina and Tencent] expressed that they would thoroughly implement the relevant regulations, take steps to reform themselves, and increase their supervision [of content].” That is very significant, especially if you’re a weibo user.

Earlier today, I wrote a piece about several different ways Sina’s real-name regulations could be evaded, and it has certainly seemed to me like Sina hasn’t been taking things very seriously. Tonight’s Xinhua report, however, may foreshadow significant changes. We don’t know what kind of punishment Sina or Tencent received, but it’s clear Chinese regulators want them to shape up, and since those regulators have the power to shut them down permanently, it’s hard to imagine they won’t comply.

Sina Weibo and Tencent Weibo have grown into massive powerhouses, and even after the real-name rules went into effect (kinda), they still have impressive user numbers. But don’t be fooled into thinking that would stop the government from shutting them off entirely to prevent the spread of rumors it sees as extremely harmful — like, say, rumors of a failed coup during a time of leadership transition. People who suggest the government wouldn’t shut down weibo because it’s too popular may be forgetting that just a few years ago, the government turned off basically the entire internet in Xinjiang, a province with over twenty million inhabitants, for months after unrest occurred there. If they think weibo poses a real threat to social stability, they will not hesitate to pull the plug.

But it will never come to that, because Sina and Tencent aren’t stupid. They may have been playing fast-and-loose with the real name regulation rules so far, but they both understand that complying with regulators is the only way a company can do business in China. (Don’t believe me? Ask Google.) So, if you’re on weibo, expect to see significant changes in the months ahead (and maybe don’t retweet those coup rumors unless you’re interested in getting to know your local State Security agents a bit better). Real-name registration hasn’t significantly impacted the discourse on Chinese microblogs yet, but I have the distinct feeling that the music is about to stop.