What a good idea! I have been putting a big "X" and that works only 1/2 the time. Sometimes the "X"and date is turned to the underside. I found two old china markers, a purple and a blue, in my art supplies. They sure work better than pencils but I don't remember where or why I got them. ( don't think I will run out any time soon though )Thank you to whomever suggested drawing a line around the middle of the egg before setting them with a broody. That distinctive mark has been much easier to see at a glance than the dates I have always placed on the eggs in the past.