I thought this campaign was over. How can I get back into the company now? I thought that if the signature is changed then this will be displayed on the panel in the personal account. I didn't realize until three days later that the signature had been changed. I'm confused 
you can't rejoin the campaign again if you left or your account became disabled for inactivity. not sure, about "I thought that if the signature is changed then this will be displayed on the panel in the personal account."
but you should always check the campaign thread you joined for updates.