What are Clan Marks?

It's either genetic and appear as a person ages or they paint them on when they are old enough, because neither T'kebbe or Khloe or any other miqo'te child have them.

The U tribe in Forgotten Springs all have the same clan mark but in different stages some only have one line while others have 2 or even 3 this could be a genetic thing as the younger ones seem to have less stripes, but also could be made to denote rank or status.

As for the first a lot of miqo'te don't have marks, and I wonder is this due to the destruction of clan lines so no one bothers to put clan marks on because they don't know what they look like or there not enough miqo'te left after the flood that 200 years of reproduction with other races have meant that those genetic markers have been lost?

Ideas welcomed.

I assume it's probably genetic and as the Sunseekers have a rigid breeding tradition with one male 'servicing' multiple females, it's probably a trait passed on from the father, hence why a lot may have the trait while some don't, they were sired by a different nuhn (some tribes actually have multiple nuhns, there is no 'rule' that a tribe can only have one, but it's usually the more larger ones that are like this, which would add greater genetic diversity in the tribe.). As far as character creation goes all facial markings can be removed if you've chosen a female character (as I did when I created my character back in 1.0), so it's likely this is quite common.

And of course it should go without saying a lot of Sunseekers (and Moonkeepers too for that matter) have left their tribes and settled in mainstream Eorzean (and by extension, Hydaelyn) society and ended up in relationships outside their tribal traditions, which may result in children with or without these traits, or forming new ones (the U tribe seems to have a greater influence from Ul'dahn customs due to their settlement being a trading post with Ul'dah), so such features may end up disappearing or appearing throughout different generations.