You can allow the possibility in any project to reject a SIGN item if you disagree with it.
In the administration, under Project Settings > DOC settings of a selected project, you can find different options to:
Allow to reject SIGN
Require a comment to reject
Allow rejecting without password
add a signature hint, a note below it to provide some explanation.
As soon as a SIGN item is rejected, if some others didn’t sign it yet, they won’t be able to sign it anymore and a new SIGN item will have to be created.