Sorry can't sign right now, because I don't have a synced Bitcoin Core version and a safe environment at my disposal right now. Would take weeks.
You don't have to be synced to sign a message, but if it's security you're concerned about, alright.
if you have any doubt that I'm the rightful owner.
It's not about being the rightful owner, but rather about being the original one.
But you can send campaign earnings to the old address
If that's ok with you, I'd accept it this way.
How about the 1H61K address I mentioned earlier?
You can use the 1H61K address or any other you find that I've posted in the past and does have some BTC on it.
(I could sign with that address if you point me to a quick and easy way to unpack a 7-Zip encrypted wallet-file, extract the private key and sign a message in a safe environment on a potentially unsafe PC.)