It may not represent just a sealer. Depends on what ammunition, and from what country. Not all countries mark their cartridges and bullets to NATO standard, and some old stuff from the US, etc, used different standards. That is, a .30-06 round from 1947 may be marked differently than a .30-06 from 1957. (Yes, I know that the military round is not called .30-06!).
Perhaps if you explain what cartridge, including headstamp, and perhaps a picture, someone could give a more definitive answer.