Ring signatures are unwound when the tax authorities require you to provide your password to justify your tax basis.
Use more than 1 wallet? Plausible deniability is such a nice toy. And why password? Give them a viewkey to whatever wallet you want to have exposed. Ideally you can even password protect a wallet with different keys who then unlock whichever viewkey you want to release, like the hiddenos feature of safeguard and truecrypt.
I am not understanding how you think this helps?
If the tax authorities demand my private keys so they can trace on the block chain from a particular tx that I claim to be my tax basis to the transaction where I am claiming a capital gain, then how does your suggestion alleviate that demand?
Since Monero has private keys, I can't refuse their demand if it is the law.
http://www.nestmann.com/could-the-government-force-you-to-tell-your-deepest-darkest-secrets
in fact I have deleted my post...
Impossible. bitcointa.lk has a copy you can't delete.