Personally, I don't care if people know I donate to charities or not, because attention is not why I do it; however, there is an exception
KIVA is a charity that puts people in poverty aound the world together w/ folks willing to make microloans to help them work their way out of poverty. When you make a microloan, they offer you the option to share it on Facebook.
I always do, because I hope the combination of the example together w/ the story of the person I sponsored will inspire some of my friends to do this
Want to make the world a better place by helping one person lift themselves out of poverty? Check out KIVA.org