You can still sign a message in blockchain.info if you are not yet go on upgrade, i just tried it now. After doing that upgrade, you can now configure the security features such as backup phrase, second password, logging in mobile phone via pairing and etc.
My problem is, how will I know the private key of my address?
I used the wallet the first day of launch, and had the same questions. I contacted support about their half-baked client, and they responded with a snarky "We will add them later, if you don't like it, go back to the legacy version."
Not to be a cheapskate, but I asked them how to do that, and they told me to make a totally new wallet and SEND my bitcoin over to the new wallet... wtf?
*Months later*
Still can't:
- Sign a message
- Export private key
- Revert to wallet v2 from v3
- Use the mobile app
- Log in using the normal
blockchain.info/wallet page
- And more