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?
It’s a cheaper version of the security-patterns you’ll find on the inside of quality mail envelopes - meant to keep snoops from being able to read what’s inside. It’s for your privacy …
… or maybe it’s just ineffective marketting meant to resemble such, or the absolute minimum/cheapest option to comply with medical privacy laws.