I'm sorry I do not understand what is growing bitcoin and earning bitcoin. In my understanding, signature campaign will pay you bitcoin that will add up to your existing bitcoin, still you are just earning it. Growing bitcoin must be you are investing your bitcoin and your bitcoin will earn some more bitcoins for yourself. Or, growing bitcoin is just making more number of bitcoins ?
You mean to say earning bitcoin is different from growing bitcoins ?
I do not think so because we can use these terms interchangeably. But, literally growing means as you said we may need to invest something but to earn also we may need to invest. So, I do not find any differences among earning bitcoins and growing bitcoins.