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Yes it does allow signing.
I don't use blockchain.info much, but the steps above do work for latest version too ! I checked yesterday only.
It's here :
You may update the OP 
Yes it does allow signing.
I don't use blockchain.info much, but the steps above do work for latest version too ! I checked yesterday only.
It's here :
Done, thanks!
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I believe it will only work for the imported addresses, try to make new address and sign a message with it!
If you make a new address in the new blockchain also do not work for sign message. It actually work for imported address. I do not know why the blockchain make this not available to sign message there with new address.I believe it will only work for the imported addresses, try to make new address and sign a message with it!
Add this as well. Thanks!