Clearly a reference to [1] but I'm too lazy to go and check if it's visible to the naked eye. If not, fun design and weird that there was no comment by the scanning folks.

[1] https://en.wikipedia.org/wiki/Heinz_57

maybe it's printed on the thin film you remove to open the cap. really dont know

Some of the heinz bottles have a small relief in the top of the cap, kinda like this:

http://flyosity.com/design/ketchup-bottles-the-physicality-o...

That's why it appears in the scan.