https://en.bitcoin.it/w/index.php?title=Special%3ASearch&search=anonymity这里面讨论了这些问题：
You might be thinking that this attack is not feasible. But consider this case:
You live in China and want to buy a "real" newspaper for Bitcoins.
You join the Bitcoin forum and use your address as a signature. Since you are very helpful, you manage to get 30 BTC after a few months.
Unfortunately, you choose poorly in who you buy the newspaper from: you've chosen a government agent! Maybe you are under the mistaken impression that Bitcoin is perfectly anonymous.
The government agent looks at the block chain and Googles (or Baidus) every address in it. He finds your address in your signature on the Bitcoin forum. You've left enough personal information in your posts to be identified, so you are now scheduled to be "reeducated".
You need to protect yourself from both forward attacks (getting something that identifies you using coins that you got with methods that must remain secret, like the scammer example) and reverse attacks (getting something that must remain secret using coins that identify you, like the newspaper example).