Anyone want to help me figure out how to sign a message?  Maybe I'm dumb, but I've spent an hour trying to figure this out on my blockchain wallet and can't.  I've read this:  https://www.reddit.com/r/Bitcoin/comments/18qy88/bitcoin_message_signing_and_verification/ without figuring it out.
I've found this:  https://support.blockchain.com/hc/en-us/articles/210353833 which states: 

"What is message signing, and how can I do that?

Message signing is a way you can prove you control a particular address, and demonstrate you have ownership of the funds.

This feature is currently only available for your Imported Addresses, but will be implemented for all addresses in the future. To sign a message, go to Manage Addresses to the right of Imported Addresses. Choose which address you want to sign, and click More Options -> Sign Message.

A small window will display allowing you to provide a unique message or signature that identifies you as the owner."

Now I didn't import an address for the transaction, so maybe that's why I'm not getting it?