In my opinion, social campaigns are not as effective as a signature campaign. Beginners and learn about ico will participate in the forum and they will feel confident when the high rank members are signed on 1 ico. The current media is quite thin, and most are non-quality ads.
In signature campaign you wear an avatar and signature of the campaign to promote and gather an investor for the project that you joined. In social media of course is also to promote but not that like in signature because the big investor and almost all people that having an interest in crypto currency will be here in forum. That's the reason why signature campaign are having a high percentage of rewards than social media campaign.
That's definitely right, almost all the biggest investors are here in crypto world/ forum as well as to promote the project the best place is here. The percentage for social media campaign is not low, maybe because there are many participants of it, that's why the rewards are low.