You should sign this if
A: You're a human and you have a soul
B: You understand how important it is to apply manners in driving in driving as well as all other social situations.
C: You have been neglected of the wave at one point and you recall how irritated and vexed you were.
D: You realize the breakdown of society in this day and age and you want to put an end to this social injustice!
Lastly...
People should sign this because it is a staple that when you let someone in, you do a courtesy wave. If there is road construction and you let someone merge over.. They courtesy wave! This can make all the difference in someone s day. Let people who do you a favor know that you appreciated it. Ther is little to no effort to do it and it's the polite thing to do.