I don't know if you noticed, but we posted at pretty much the same time. I was responding to your previous post. And I agree with you: I don't think I've ever seen a character with this symbol on their portrait, except via the Children's Crusade.
What I was trying to say in addition was that there is slavery (in the modern sense of the word) elsewhere in the game, it just uses different mechanics and it's not explicitly described as "slavery".
(If you want an example that affects visible characters, how about the ability to take/offer concubine/consort from your prison, which breaks any existing marriages, and which the prisoner can't refuse? Unlike most adult characters, a consort/concubine cannot leave of their own free will, but their partner is free to give their concubine to someone else.) (Or, another example, if you capture some young children after a siege, you can keep them in your prison, brainwash them but also educate them, and in the end you get high-skill commanders/councillors/spouses.) (There are probably other examples.)
