This video, called Why Danger Symbols Can’t Last Forever, describes the process used to design common warning signs that will need to last for centuries or more (in radioactive areas, for example). However, the meaning of these symbols can change over time as associations develop between them and more lighthearted ideas, such as the association of a skull and crossbones with pirate treasure. Therefore, designers came up with alternative ways of warning against danger, such as spikes to create a threatening environment surrounding the radioactive area, visual depictions of what will happen if a person enters, or organizations specifically tasked with passing down knowledge.
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