My Friend told me you can join only one campaign at the time
Create more acc to join multiple signature campaign
But you can join multiple facebook and Twitter campaign at the same time
Creating more than one account just to spam join signature campaigns is frowned upon here in bitcointalk. Not to mention creating more than one account means you have to post twice as more, hence most likely significantly decreasing your post quality. I'm not 100% sure, but I think the admins in this forum has a way to affiliate your main account to you alt accounts through your IP. I'm also not sure if campaign managers has access to this information though.
Also, enrolling on signature using multiple accounts are not allowed on most(if not all) signature campaigns. Here's one of ChipMixer's rules:
5. Enrolling alts will result in both of your accounts removed without payment.