Public signs are mostly straight forward. They often have a critical role to warn people to avoid a dangerous situation, so designers have an obligation to send a clear message that is quickly understandable by everyone.
The illustration of an electrically-shocked man creates alert that makes you never want to get closer. The warning sign at power plants vary in different places, but the electrically-shocked man is almost always there. It’s just the visual makes the point well.
There are also signs that make you smile.
Left: Handmade parking sign at a post office on Salt Spring Island, BC Canada.
Right: Sign for protecting a rare kind of frogs in Hakodate, Hokkaido Japan. The frogs cross the road to get to the pond across the street in their breeding season, and they often get hit by a car. This sign is a part of Ezo-Hikigaeru conservation program by Hakodate Rotary Club.
Finally, here is another handmade sign I found in my neighborhood sending a very clear message.