Signing a Message
Step 1 -
First of all login to your wallet and click Settings Tab on your left navigation bar.

Step 2 -
Click on Addresses under Settings Tab, Once you did you will see your address section in the center of the page.

Step 3 -
Now, Click on Manage Addresses infront of Imported Addresses section.

Step 4 -
You will see all your addresses associated with your wallet. Simply click on More Options on the right side.

Step 5 -
Click Sign Message and you are done!