I've been digging into older notes recently and noticed a strange occurrence. Many notes from the mid 1800s and earlier have an intricate pattern on one of the edges. The wierd thing is that most of them are cut, whether it be a straight cut or a wave of some sort. I assume they're some form of security feature or tell that a note is still valid, but have no concrete information. They must have a name and specific function since they're used so often. Any info is appreciated, thanks for reading!
It's an anti-counterfeiting device. The bank (or other authority) that issued the note would keep the stub that was cut off at the left side, and that stub would have a serial number matching the number on the note. In case of a suspected counterfeit, they could match up the note against the stub and see if they fit together perfectly or not.
Yes, I would agree with @Numbers that this was part convention & partly security. Here's one source of info on your 4th Zaragoza 100 Reals note. According to Numista many Zaragoza notes were left as "remainders" (not issued/not cut) in sheets. I would try using Numista or the Bank Note Museum (BNM) to identify them (if you haven't already).
It's called a counterfoil, and serves the same function as a perforated ticket stub where two parties each get half of the total ticket.
Used to protect the holder of the note against a counterfeit note. The stub that was cut off of the note could be matched to the note for security and to check it’s authenticity.
