It's stupid to leave a signature campaign before either letting the manager know that you're leaving and wait for his approval, or at least wait for the post count to be done.
I know it was my stupid mistake and i am guilty of it.
All the managers here have a great understanding and if you ask the manager of your upcoming (joined) campaign for which you left your older one, that you need some time till the post count is done and you are allowed to remove your signature and avatar, I am sure he will understand your position and will reserve your spot till your week ends in your (old) current signature and allow you to join once you get paid there.
That's why I see 'reserved' frequently appears in many signature campaign spreadsheets in the list of participant names.
I done this type of mistake because many campaign mangers says in their reply "wear your signature and avatar within 24 hours" I think it's a deadline after this i cannot allowed to participate.
but now i know how it works it was simple but i was unlucky to not getting paid for 2 campaign because of my simple mistakes.