Welcome to the forum.
You only get the mark when you've held them recently. And it only lasts for 6 hours and you can't have two dragon marks at the same time. If a dragon is sitting on your shoulder, the mark will last for 24 hours but you can still only have one mark at a time.
Do you use mods or anything? Have you cleared your caches? Are you using dragons that you got already hatched or dragons that you hatched from an egg?