I used to have in my email signature:

P.S. Don't forget to save the world.

followed by a link to some form of online activism. For example, the Hunger Site, where the click of a mouse can donate a cup of grain.

Yesterday evening marked the first night of Passover or Pesach.  It's kind of a blessing when my UU church's annual observance of Pesach actually takes place at the right time.  (All Souls does a wonderful Seder dinner but it plays a little loose with the rules... which is very UU.)