Affirmation
Every day, I get ten or twenty messages from various political causes, asking me to sign their petitions online. (Email filters take care of these, but I occasionally check the folder out of morbid curiosity.) My suspicion is that these "petitions" are nothing of the kind; they influence nobody and are easily forged (why not simply grab the voter rolls of the appropriate political party and plug them into the petition template?). My surmise is that they are designed to confirm your name and address in their databases, to tell them that their emails are reaching you without going the transparent-GIF route, and to use a psychological principle which, I vaguely remember from back in undergraduate psychology, was called "affirmation." That is, if you are induced to do a little, trivial thing in support of an idea, person, or cause, you are then much more likely to do something larger, like contribute money, out of an unconscious sense that you want to remain consistent with your earlier action. It no longer works, I'm afraid, and the messages have gotten shriller and shriller with their "the sky is falling" messages, such that now, when the sky actually is falling, they've cried wolf, and, I fear, it is much too late.