I will keep this short, I have some work in line to do. Just spotted the topic and thought to leave my thoughts here.

Not always. Ex: Livercoin, Yobit.

Honestly speaking the privilege thing is not always right only for the participants. Sometimes a campaign management feel privileged when they can hire some particulate forum members. Ex: Suchmoon in ChipMixer, some other users in ChipMixer and also various campaigns.

In this forum, although we do not know (99.99% cases) anyone by facial or in real life but every user has their own image, their own personality. A user born when they join and their forum activities build up their character. Ex: If I mention game-protect then we know who we are talking about, if I mention yahoo - he has an image, me has an image, the OP has an image. Similarly almost all the users has their own images and in a signature campaign, the image of a user reflects their worth. Everything has it's own price.

So, I kinda slightly disagree on saying "Signature campaigns are a privilege". It's an opportunity for users to get some financial benefit with the things they already are doing and from the companies perspective - it's a way to monetize the traffic of this forum so that they can build up a business. Both party are getting benefited.