Well my honest opinion is that it is kinda rude. Most people would just read this and immediately go sign up as a ninja. But hey, what did you expect - it's not like it's much different from the rest of the society anyways!
I wouldn't say it is rude or fooling anybody. It is just being playful, there is a place where you can get more thanks if you sign up as a ninja so I don't see anything wrong. Members can read all about the perks of becoming a Ninja and decide whether they want to or not. No one is pressured into joining if they don't want to.