Do the admins accept signed ETH messages as proof of ownership of BT accounts? I think they only accept signed BTC messages, anyone knows?
No, admins only accept signed messages from staked btc address as mentioned in
this thread. Theymos and Cyrus are the only charged to do so. For some other moderators, signed messages from altcoin addresses can be used as proof of ownership if you get in unexpeted trouble that needs to freeze the account, so you can un-lock it.