Here is a msg I signed with it back in 2016:
mill0601 from bitcointalk today is 6 nov 2016
-----BEGIN SIGNATURE-----
<15d4cdy9TgUyLstnVf7MDDaPK5tM6UepKH>
-----END BITCOIN SIGNED MESSAGE-----
now don't say that I have copied it from somewhere. I have copied it from my account's inbox. I've signed it back in 2016. but never posted it in public.
--snip--
How would this message proof anything? Signing a message is providing proof that you are in still control of the same wallet you used to generate an address that was staked a long time ago. You can't proof that you are the same person who staked an address by providing a message that was timestamped 4 years ago, and was found in an inbox...
If a signed message is asked, this means that you have to create a new message with the current timestamp to proof without a shadow of doubt you still controll the same wallet. In this case, this message only proofs you have access to the inbox of this account, acces you would also have if you hacked or bought the account (i'm not saying this is the case, but i am saying that the signed message proofs nothing at all).
If you want to proof anything, provide a signature for the following message:
mill0601 from bitcointalk today is 7th of januari 2021. Message signed for bitcointalk thread 5306741
-----BEGIN SIGNATURE-----
15d4cdy9TgUyLstnVf7MDDaPK5tM6UepKH
create valid signature here=
-----END BITCOIN SIGNED MESSAGE-----