I am wearing a free-of-payment signature, but what do you mean "they want to advertise for free (even if they know how to gain from it)" ?
I would take it like this, why they need to spend money if the users are willing to wear the signature for free?
Sometime I think wearing signature for free has a drawback, it make the project get free advertisement and it could influence the project to pay lower, because it's easier to make people to wear the signature. If someone wearing non profit project signature like Bitcoin site or donation, it's fine, but not for other thing...