Sign and Verify Messages
You can sign a message using the CLI sign_message command like this
sign_message <"Your Message">
The signature will then be printed to the screen. You may then provide this signature to someone else to verify. The command to verify is:
verify_message <"Your Message"> <address> <signature>

Try it yourself

You may reproduce those steps and make sure you get the same results: Create a wallet using the seed
dodge ouch present sake aquarium mystery woken cell aztec duplex inundate vogue vinegar afloat rumble aphid siren sowed junk otter potato argue banjo bays duplex
(do not use this seed for anything else except this test)
Open this wallet and type sign_message "My Message"
This is your signature. Then verify the signature:
verify_message "My Message" QWC1LxPvCVibmBUAaJu1hm8xk35UjJqYvTA4AisTSerheZ53Yse3SwAg8U7WkPcDAxZH1QpqDVxBcKvDUmMUuRJuAEZa9HzZm9 SigV1fYJ8t1rf4UkNATJFK7fxmJAcg9GCBGG9dXrr7bs4KZNBjnFgNJ33256MFRX7AG2q1Kdi8XQDruMkZbiNwXwAsLb9
Valid signature from QWC1LxPvCVibmBUAaJu1hm8xk35UjJqYvTA4AisTSerheZ53Yse3SwAg8U7WkPcDAxZH1QpqDVxBcKvDUmMUuRJuAEZa9HzZm9
If you sign this text yourself you will probably get a different signature than me. This is because the signing is not deterministic. Nevertheless, you should be able to verify my signature without problems.

Sign & Verify using the GUI Wallet

    Create a new wallet from the example seed above
    Navigate to File > Sign message Write My Message in the the message field at the top.
    Copy the generated "Signature" into the verification field (Verify message) or navigate to File > "Verify signed message" Copy the message into the verification "message" field. Paste the Qwertycoin address in the "Address" field Your Message will be verified.