It wasn’t that long ago that some people would use two pens: one with black ink for everyday stuff like writing notes and making annotations to documents, and another with blue ink for signatures. The belief was that the blue ink added a level of security to the document, and if a letter had a signature in black, it was a photocopy. This was an adequate system at the time, but not convenient or secure, especially when scanners and computers became commonplace.
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