Can't set signature (doesn't apply)

Can't set signature (doesn't apply)

Hi, I'm trying to set the customized signature for domain thetinglymind.com but it doesn't seem to work. Even when I compose a new email and use the insert signature option, a box shows up and says there's no signature even though I have set it up and even checked the box for my email address. Could you please assist me with this?

Thanks,
Ellen