MyBB Community Forums

In conclusion:

• When you click update signature, your signature is updated. In all the posts that have your signature enabled it will be visible.
  
• If you have selected no action then the posts that show/don't show your signature will not be modified.
  
• If you select enable signature then all posts will be set to show your signature.
  
• If you select disable signature then all posts will be set to not show your signature.
  
• If you press preview signature then no changes will be made, except you will be able to see what your signature looks like when parsed.
  

The preview facility is there for when you want to see what your signature looks like but don't want to change it for users to view.

"If you have selected no action then the posts that show/don't show your signature will not be modified"

That is what I was saying since the begging it does update signature in all posts!
Try it yourself.

Anyways I probably don't understand hoe it works so this thread could be closed!

Say this post here I selected disable signature. If I update my signature with no action then in my post above you will see my new signature but in this post you will see nothing.