I want to change my "signature"

[temery]

Same: "Your full account details are not currently editable."

what are you trying to add to your signature.

 

[Moontan]

While I get the same overall "Your full account details are not currently editable." message, I'm able to change a lot of things, including my signature.

Have you clicked on "Signature" in the Settings to actually try to change it?