How to sign a message in Counterwallet?

Pick the address you want to sign a message with, go to Address Actions > Sign Message.

I didnt think that signing messages was working on Counterwallet, has something changed in which you can do this now?

This works certain things, but it doesn’t for all.

Since you’re probably wondering about things like LTBCOIN address validation, that probably still doesn’t work but it’s a 3rd party issue that we reported upstream a long time ago.

For this kind of purpose a workaround is to export the address’s private key, securely import it to another (Bitcoin) wallet, sign a message there, and then remove the address from that other wallet or remove the address, if you don’t intend to let it have access to the Counterwallet address).

Additional information and workarounds:

For now I think the best solution then is still the companion wallet by @loon3