In the average signature campaign to pay the participant is with bitcoin, because it is not allowed by the forum to create a signature campaign paid by altcoin. There are also paying bitcoin and altcoin like this signature campaign https://bitcointalk.org/index.php?topic=3170747.0  the manager paid participant with BTC and IOST. But for those who pay altcoin is in bounty campaign, like me who joined with bounty campaign and paid with byteball (altcoin).