This would be a good address to use to sign a message to prove ownership. Since it holds 0.5 BTC, you can be pretty sure the address hasn't been sold with the account.
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But whose ownership would it prove?

If Habbear signs the message, he is also showing that the Myfe account had been (is) under his control.

If Myfe signs it, well, it does also prove the multiaccounting

If they both provide some willy wonka argument as to why they can't access the address.... it's 0,5BTC! So it'd be safe to assume both accounts changed hands

And the same happens for the 1GJL2m5h7oMakRsdaQT3QQ4XzyFnKQwbCQ altough it has no funds