Some egg graders in Ontario will stamp their egg with a code that conveniently gives you access to the best before date, just in case you no longer have your carton. The code can also include an identification number that can be traced back to a grading station.
During the grading process, after eggs are washed, candled and weighed, they pass through the stamp chamber where the stamp is placed by inkjet onto the eggs.
The ink is approved by the Canadian Food Inspection Agency, so whether you are boiling, scrambling or cracking your eggs, you can feel safe knowing the vegetable-based ink used is 100% food safe.