If it doesn't say a period of days then it's likely permenant.
The bit.in campaign seems to get a lot of signature spam banned accounts.
Yeah, I wish they'd pay more attention to their participants or not allow newbies. I've seen many people get banned then just re-sign up again and back on that campaign.
Now you are evading a ban, THEYMOS UNLEASH THE BAN HAMMER ON THIS BITCOIN PEASANT!
They're usually allowed to post in here only.