I wouldn't bother. The amount you can earn from these campaigns are quite small, even for Legendary ranks.
I don't think no one will harass you for such a unusual income that no one is sure about.

Bitcoin is largely unregulated in the world and it will be difficult to regulate it once they make a significant effort.
This amount is also pretty small, so I don't see why someone would really care, as the whole signature campaign economy is very small.

But then again, I am not a lawyer, I have no idea.