It's very unfortunate but such an obvious case it falls to the campaign manager, they're being paid to prevent such basic scam which includes verifying that the user is wearing the signature.
Therefore, @Hhampuz and @Royse777 must compensate the company for the past weeks or at least pay to developer (out of their own money) to create a bot to verify that users in the campaign do not modify them signature during the campaign period, any modification will be sent to the campaign manager.
It depends how you approach this.
What would you say if you were paid to hire people to hand out leaflets every day for a week, and one of the guys would take leaflets from you every day in the morning, hand them out for an hour or 2 and then throw the rest into the bin and go home? Should you be responsible to the company for what happened? Should you stand there and watch the leaflets being distributed every single day for 8 hours?
Managers are there to hire people, prepare signatures, count their posts and distribute payments. They aren't all seeing gods that cannot be cheated and they cannot be there reading people's posts as they make them.
Anyway, I guess I made a bad assumption once again. I always thought campaign managers used some kind of bot to make sure that participants never changed their signature. So it would have been possible for someone in the Chipmixer campaign, for example, to change what was in their sig space for a time as long as nobody noticed? Wow. I've had the aforementioned assumption in my head for years.
That was the case in campaigns run through automated software. Maybe you remember the old bitmixer campaign run by Lauda, or the yobit campaign that required you to connect your exchange account with your bitcointalk profile ID. If I'm correct, these were actively monitoring if you had a signature.