California gets a lot of trash talk from the knee-jerk crowd though the knife laws aren't bad. But you cannot conceal a fixed blade, period. There is no percentage-concealed in any ordinance I have read, that one goes right in the urban legend trash bin with the "if it's not longer than your palm, then the length is fine" bit. I think the urge to carry scout-style sometimes come from the urge to work around no-conceal issue by having the blade not visible to anybody from the front. The logical corollary is that one is laying in ambush. Behind the back sheathing can also lead to comedy gold and interesting scars as well.
The only time I have ever seen a karambit in the wild was on the belt of a homeless teen girl. It was $10 MTech piece of junk, but it was right there out in the open. Anybody who wanted to mess with her knew that the stakes were a lot higher if she got a finger in that ring. It probably saved her a lot more hassle the same way that brightly-colored snakes don't get bothered a whole lot in nature.