Here's my tutorial for changing your sigs and adding a picture to it.
Step 1: Go to settings at top right.
Step 2:While on this page, go to Edit Signature under My Settings.
Step 3
ut whatever you want to be your sig in the box titled "Edit Signature"
I hope this helps
Step 1: Go to settings at top right.

Step 2:While on this page, go to Edit Signature under My Settings.

Step 3

I hope this helps