Quick & Dirty Charitable Hack

I'm confused about how this works.

You add a line to my outgoing e-mails. This contains a link to a charity, and boasts about how many people have seen/clicked this link, but doesn't name the charity or give any real reason to follow the link. (“Donate now!” is not a reason when you don't state who the donation is to or what it will be used for. It doesn't even say that it's for a charity.)

How do charities gain from this? Is the link to a donation page on their website?