It depends on the campaign whether they want to reward the most in a certain social media platform or in the signature campaign, but mostly in the bounty there are only a few who is looking for a signature campaign, as they commonly looking for telegram, youtube and Twitter, you can check it in the bounty section.
All campaign have the same reward I think, social media campaign or signature campaign just participant in each campaign why make reward little than other campaign. Signature campaign have limited participant and got higher reward than social media campaign, looks almost bounty have two thousand participants from social media campaign and signature only have maximum above two hundred participant, this why make reward higher signature than social media campaign.
Signature campaign participants get more tokens because there are fewer participants compared to social media campaigns. Some bounties do allocate more tokens for signature campaigns due to the large number of forum visitors and this provides an opportunity for the project to be recognized by the crypto community