I don't know if this is a good idea but maybe the OP can try use the
brainwallet for the job.
When you sign a message, follow the link above.
Just Click on the Bitcoin-QT button, copy-paste the address, message and signature, (
be careful with the spaces!!!) and if you get the green label on top with the
Message verified to be from <YourAddres> then you can just click on the Signed Message button and copy the finished message format from there.
And see how it looks like in the link below >
Edit: You can verify it
here~
So my address singed message should like that :My account <account name> has been hacked/lost. Please reset the email to <my email>. The current date is <today date>.
Not anything else, ex:: This is my address I am owner
No need, if you sign a message from an andress that makes you the one controlling the private keys so basically you are the Owner of the address (if you haven't shared your pr.keys with someone else which will be a stupid act). Posting this from your current accout is enough evidence.