Why does American money have small numbers on the back as if being numbered?

I noticed that on the back of any american bill there is a small number on the right side of the bill.Why does American money have small numbers on the back as if being numbered?
The little numbers are the plate numbers used to print the bills at the Bureau of Printing and Engraving.Why does American money have small numbers on the back as if being numbered?
um i never paid attention to it but now that u mettion it i looked and i did not notice any number on the back except for the dollar camount the number i have noticed is on t5he right side in the front of the bill i believe that there the nubmer of what order they were printed fr that year each year so many 1 5 10 20 etc are made and each one is numbered and i believe its basically how many bills are made pure sheet of paper etc
It's a serial number. It's used to trace the origin of the bill, it helps to identify forgeries and also can be used for example to help track down bank robbers and kidnappers
So you can't contefiet the bill.

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