They are correctly named printer's marks.
Printer's marks are industry standards and are automatically produced by professional software prior to making printing plates. DO NOT attempt to construct your own artwork as it may mislead professionals who depend on the reproducibility of the design configuration.
Each design serves a specific and particular press function.
There are many different marks for tracking quality or for indicating operations that will be used in finishing the printed piece. Printer's marks are used to indicate the printed area, the area to be trimmed away from the finished piece, scoring, folding, punching, corner-cutting, die-cutting, drilling and other assembly.
In addition, the different patterns and colours can be used to troubleshoot press problems and also to ensure colour fidelity.