How to cryptographically sign a message

Here's how you can sign a message cryptographically. This is needed for art contest winners, but is useful to know in general too.

1. Go here.
2. Allow access to the Polkadot JS Extension. (Don't have it? Install it here)
3. Pick your account and enter the message into "Sign the following data"
   
4. Click "Sign Message"
5. Enter your wallet's password and confirm
6. Copy the resulting signature by clicking the "Copy" button:
   

Success, you signed a message.