On the cover of some older comic there is a triangle or shield with numbers in it. What do the numbers mean?
These were called “triangle numbers” or “shield numbers.” The lower, boldfaced number indicated the order in which the stories flow. Because the story line sometimes flowed continuously from title to title each week, it is difficult to otherwise discern in which order the comics should be read. For example, issue numbers do not indicate whether ACTION COMICS #761 precedes SUPERMAN #153, but triangle numbers (4 vs. 5) show that it does. The top number is the year; triangle numbers started over at 1 each year. Triangle numbers no longer appear on the regular titles.
