I was backreading some topics in Marketplace and found out that signature campaign was not included in the first service of this website... What if Signature Campaign was never introduced... What else could be the Service we can apply for?

Only unskilled,lazy idiots would suffer.Developers,graphics designers,artists,marketing professionals,SEO guys,Computer Science Engineers would still find themselves freelance work for bitcoins which pays much higher than signature campaigns.On the brighter side,forum would be a less crappy place to hangout.
Nobody would suffer. It's just a side income and should remain as such. If somebody stops paying you for posting will you suffer? Like literally suffer, being unable to pay your bills?
Signature campaigns were introduced somewhere in 2013 or around that date. I saw Primedice campaign with posts dating back to 2013 and it was one of the first such programs on the forum. It got them some nice returns and helped build client base, so other startups followed the same path.