Japan is surely one of the politest places you're likely to visit. If you ask someone for directions, there is a good chance they will walk you there themselves. Behaving honorably is an important part of the culture and there is never a lack of signs, often cleverly illustrated, reminding the public of what is expected.
One of the most interesting and clever examples I found is produced by Japan Tobacco. In smoking areas, on trains and near ashtrays, there are often signs related to smoking and behavior in crowds. Notice the minimalist illustrations and the strange-but-effective messaging from these examples.
This is my favorite. The proper disposal of cigarette butts is an important issue. Meet. Love. The End. - A timeless story.
Some are designed (I think) to promote awareness of how non-smokers perceive smokers.
But, it's not just focused on smokers. On trains you may see signs about proper train behavior. For instance, apparently public grooming is discouraged. Make up - Image down.
And those backpacks. I have been in violation multiple times.
Unexpectedness, emotion, concrete examples, these signs are right from Made To Stick.
You can find a gallery of over 70 of these signs via Conbinibento and some particulary funny ones at InOnePunch. I've been collecting strange signs from all over here and don't forget Darren's Hall of Technical Documentation Weirdness.
Bonus sign - a mission statement in Engrish, from a bakery at a train station in small town Shikoku, Japan:
Good quality cumbustion setting up is very important for me, personally.