In the previous article about the packaging symbols we explained what they are and how to use them, especially focusing on those one referring to consumers. Today we will speak about hidden symbols instead, that means technical marks situated in no visible areas, that are generally aimed to the ones working on packaging manufacturing and packing.

That kind of signs are usually placed on the glue flap of boxes, if any, so that they will be not visible when the box is assembled, or, in others cases, within the most hidden areas of packaging.

Technical symbols help reduce risk of errors during the packaging production flow, making management and control processes easier. Based on the typology, they have different purposes.


Hidden symbols: type and use

On some packaging you may find bar codes, of different types and widths, that can have three functions:

  • to verify the conformity of packaging within the production batch to avoid mixing up the boxes;
  • to control print quality by checking symbol quality;
  • to control cut-off and sidelay register, checked based on the distance of code from the edge (if it is homogeneous or not).

bar codes


Instead, colour press marks are used for colour quality and intensity check; they are realised, in fact, both through the colours of the graphic artwork and their corresponding grayscale.

colors marks


In the pharmaceutical industry, it is mandatory to avoid mixing-up, by checking colours so that similar drugs or with a different dosage will not be packed in a wrong box. In this sector, danger caused by that errors is really high, that’s why any manufacturing phase must be accurately supervised.


Crop marks are typically placed on internal flaps of the box (ideally on the background). These registration marks are used to exactly align the sheet and the colour plates, during the printing process, and to properly insert the sheet inside the cut machines.

crop marks cutoff



Besides technical hidden symbols there are other that, if necessary, may be very useful, first of all those one anti-counterfeiting.

Any product, in fact, can be distinguished through trademarks, serial numbers, symbols or appropriate colours in order to identify and authenticate it. Due to their purposes, they are accurately hidden and, sometimes, are realised with special invisible varnishes (e.g. StealthCode).

The same marks can be used for product traceability regarding origin, property, production batch, printing date, etc…


Other alphanumeric information, like the ones referring to the artwork position on the printing sheet, can be included in order to better manage possible non-compliance about the print, making the position of the artwork in the sheet easily recognisable.


The use of the above-mentioned symbols is not mandatory; most of them, in addition, are supposed to be read only through specific machineries. Though, using them may be very useful while producing packaging.