EDIT: Issue should be fixed now.
If you have a signature set, go through all your old/previous posts. Click "edit" and then tick the box at the bottom that says "Attach my signature". This only applies to old posts, you won't have to do it for posts you make from now on.
If your signature still isn't showing up, follow the instructions below:
-First of all go to your profile preferences and make sure "always attach my signature" is ticked.
-If it IS ticked 'Yes', then change it to 'no', click save, and then change in back to 'yes'. Just to refresh the system.
-If your signature still isn't showing up after this, PM me and I'll take a look at your profile setting from the Admin panel.