Bitcointalk.org is not subject to Hong Kong / China jurisdiction, so would not be required to produce data in any case. If some police wants data without a subpoena, they have to convince me that a serious non-victimless crime (eg. scamming) probably occurred. I certainly wouldn't help them if it looks like they're going after political enemies.
But if you're in Hong Kong or other dangerous places and you're worried about this, then you shouldn't trust
anyone to protect you: not me, not anyone. Use Tor everywhere, and on bitcointalk.org practice the
privacy-enhancing measures mentioned on the privacy page.
Serious question here, and this may be something that has been discussed at somepoint.
What jurisdiction is the forum under and under what circumstances could you be forced into providing information relating to a forum user? Like if you were living in the US and then a subpoena came by forcing you to provide the information, I'm not sure there is much way to avoid it.
Different story though if you're in a country that doesn't listen so nicely. That's not me saying to tell everyone on the forum exactly where you live or anything like that, just want to know how this would normally work.