This wikipedia page will tell you what the saftey pin is, and has a picture. It goes on to say there was an ancient version invented by the Mycenaeans during the 14th century B.C. But that one was lost in time until the modern reinvention in 1849.

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At this rate, by Tuesday it will be Thursday; By Wednesday, it will be August and by Thursday, it will be the end of existence as we know it.
- Prof. Farnsworth.