Many signature campaigns have members posting in Spam Megathreads^*. Those threads are only used (not read!) by spammers, posting the same things over and over again to increase their post count. I've never been in a signature campaign that pays for this, and I encourage all other campaign managers to stop paying for this too.

Examples of Spam Megathreads:
Is this for real? I could be a millionaire?
Teach Bitcoin in schools! [deleted]
How to be rich in gambling? [deleted]
Do you know anyone who became rich because of bitcoin? [deleted]
How does bitcoin helped me financialy [deleted]
how can we make PROFIT from Bitcoin? [deleted]
How do you Panic?
Does your family know that you gamble with cryptocurrencies? [deleted]
How many ways are there to earn bitcoins?
are people using bitcoin really to buy things? [deleted]
Why is Bitcoin so expensive? [deleted]
How big is the influence of bitcoin on your life? [deleted]
How do you deal with loss?
What is Bitcoin to you? [deleted]
How do you earn BTC? [deleted]
WHY DO PEOPLE DEPEND ON BITCOIN [deleted]
Who can destroy Bitcoin ?
Bitcoins To Cause Unemplyoments [deleted]
can we use bitcoin for buy a house ? [deleted]
Is Bitcoin giving HOPE to us? [deleted]

^* I'm not sure who came up with this term, I saw it first used by DarkStar_