Why there isn’t in my User CP panel a link for modifying my sign?
On the User Control Panel, just scroll down to Settings and Options. There is an Edit Avatar setting for your sign. Or there is an Edit Signature setting for entering quotes and such at the bottom of your posts, if that’s what you are meaning.
Edit: There is a FAQ (frequently asked questions) setting on the blue bar below the WW2 in color logo. Click on that and it has info on how to use profile settings.