This is the problem in this forum, people only looking to make some dollars without any real interest in the crypto world.
This said Horizen has never run a signature campaign (ok only 1) and it is still doing well over the months
I think it's combination of the interest of crypto world and making money. In general most of people became interested in crypto to make money, that's why now when the prices fell - this number decreased.
As for signature campaigns - even though I took part in lots of bounties in past, it's hard for me to evaluate it's effectiveness.
i remember one CEO of successful ICO said in the beginning of year :"Bitcointalk is not important, now Telegram rules" and they didn't have bounty
but after later when their token was on exchanges they decided to make promo campaign, and spent $170K for signature campaign and steemit, reddit, etc. it didn't give much result as it was organized unprofessionally and as I think it was a waste of money (token price only fell, but may be not because of bounty hunters sold tokens, but because of general market situation)
But in general I think signature campaign are good thing) People just need to consider them as small bonus but not as the ultimate goal
if the project is really quality, the bounty campaign participants may be interested and become part of the community. and this is very important for any project.