The timeline on Sina Weibo, China's popular Twitter-like service, is filled with pithy comments about "Beijing Fashion Week," chronicling the comings and goings and sartorial choices of the elite.

But the commenters aren't fashionistas, and they aren't talking about supermodels or design stars. They are referring, in not-so-secret code, to Communist Party officials.

"Beijing Fashion Week" is a thinly veiled, sarcastic commentary on the Communist Party's annual summit, now under way in the nation's capital. And many of the assembled are making it easy to be ridiculed by showing up in luxury garb — a far cry from the staid image they aspire to project.

Yes, there are scattered, unabashed criticisms of the elite on Sina Weibo, China's most popular and active microblog service. But subterfuge like "Beijing Fashion Week" helps China's netizens feel safer about mocking the country's all-powerful ruling class.

It's becoming a familiar dodge on Sina Weibo, which functions similarly to Twitter and invites quick, frequent updates — but unlike Twitter, the bulk of whose members are in the United States, does not operate in a country where political speech is protected.

And all this may change in the face of a new, more stringent policy designed to clamp down on free expression where other methods have been less successful. In a move to exert greater control on citizen speech online, the government is requiring that Sina Weibo and China's other microblogs register the real names and identification cards of users in several cities. Those who do not register this week in many major cities like Beijing will not be allowed to share or forward posts; after a period of testing, the policy will go into effect nationwide.

Microblogs caught fire in China just as they did in the US: more than half of the nation's 500 million internet users have accounts. Like Twitter, China's microblogs play host to lively discussions, with pop stars, professors and even government officials and police officers logging on daily to talk about a wide variety of topics. Most posts are apolitical and trivial: cute cats, celebrity gossip and the latest in "Linsanity."

Since microblogs operate within the bounds of the Great Firewall, they are subject to highly sophisticated and nuanced forms of censorship recently chronicled in a Carnegie Mellon study on Sina Weibo.

Censorship depends on a combination of search algorithms and hundreds, if not thousands, of people actively looking for violations. If you post about a topic deemed sensitive, it could be taken down swiftly, and without explanation. If you search for a sensitive topic, you will get a terse message notifying you that “Due to relevant laws, regulations and policies, search results are not displayed.”

Despite these challenges, many still make efforts to post critical messages, which are scattered amidst the plethora of apolitical posts. Clever users rely on code words, pictures, image-based text and viral memes that evade the keyword algorithms and pass undetected under the watchful eyes of censors.

Last year, for instance, when the bearded artist Ai Weiwei was detained by authorities and made headlines in the West, his name was quickly scrubbed from posts and searches within China. But just as quickly, many slapped his recognizable face and iconic sunflower seeds on their profile pictures and in viral memes. The images — which search algorithms cannot detect and which are remixed too quickly for most human censors to catch — continue to appear online.

Most famously, after the high-speed rail collision this past July in Wenzhou, netizens organized online to demand transparency in the investigations. In previous years, the incident may have been quickly swept under the rug by state-controlled media. But with the advent of microblogs, the topic trended for days thanks to startling pictures and viral memes. Top officials from the Ministry of Railways were sacked and the party was forced to issue an investigative report on the crash.

And not all the criticism is directed at the Communist Party. For example, after multiple failed attempts to contact Siemens about a defective refrigerator, blogger Luo Yonghao invited his followers on Weibo to rally around a public smashing of his refrigerator in front of the Siemens corporate office.

Indeed, Sina Weibo and other microblog services have opened up a space for public discussion that rarely exists anywhere else in China, a country where police quickly suppress public assembly and the state has final say on all media publications.

All of this may change in the face of real-name registration–a new, more stringent policy designed to clamp down on free expression where other methods have been less successful. We have no doubt that netizens will find creative ways to circumvent the chilling effect of this policy. Many have already begun discussing possible strategies. Even so, real-name registration will almost certainly limit the spread of politically sensitive messages, as it will be easy to trace their origin.

Even worse: the policy also threatens the vast majority of people who are not aware of or do not engage in political commentary. Just as many Facebook users now think twice about what they share online — even if not particularly controversial — real name registration may dampen the fun of microblogs as a casual place to let out some steam and relax with relative anonymity.

Microblogs have become a particularly lively, important and rare forum of public discussion in China. Real-name registration threatens this. And that is a major cause of concern for anyone hoping for a more free and open internet here.

Opinion Editor: John C. Abell @johncabell