The patch is small, about a fingernail in size.
Elsewhere on the packet they used two colors of ink: a very dark blue (this) and a lighter blue. I expected it to be some kind of alignment pattern, but only one of the inks seems to have been used here, so that's not it...
What is it for, why would they bother printing it? An ink+paper resolution/absorption test?
Maybe something for checking the calibration of the high speed cameras on their assembly line?
My guess is the cameras use it to make sure the color plates are aligned properly. A lot of packaging printing still uses a 4 step printing with one plate for each color in CMYK.
Makes sense to me. Honestly can’t say I’ve seen that one before and I’ve seen a lot of printers marks… so I guessed at the high speed bit because that’s a bit newer than most of the stuff I’ve been trained on.