By doing this step you have to donate to their stream which you can find on twitch or donate skins to their trade link, it can be a $0.50 skin with the text "please sign my profile" same goes for twitch, you don't need to donate them $100.
See picture for example

Some pro players do read their comments on their profile, so if you ask politely if they can sign your profile, they will most likely sign your profile!