how do you add signatures?

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i have noticed on a few websites like makemoneykingdom, and goldage there is a thing where you can add their signature or something like that and they will pay you to do that every month...i just don't know how to do it really i have had people try and teach me how but i just don't get it...i was just wondering if anyone else does this and if you do if yo ucould try and explain to me how all of this is done...if so i would be so thankful!