I haven't been around ducks since I was a kid many decades ago, and that was limited. Chickens and ducks can have some similarities but can also be different, like cattle and hogs can be similar in some ways but different in others. I don't have anything particular but be careful reading something about chickens and assuming ducks will be similar.
How many ducks are you talking about and what information do you want? How early do you want to mark them? My experience is with chickens but the basic marking methods should work for ducks. Yeah, I just violated my warning. I have not tried this technique but toe punching is one method. Chickens have webbing between their toes. If you punch a hole in that webbing between certain toes on a certain foot that is supposed to be permanent. You can punch holes in more than one webbing on a foot and they have two feet so you may be able to store more information by toe punching than you'd initially think. It might be a way to permanently mark them at hatch. I've never heard of that being use on ducks though. You would have to handle them to see the marks.
I'm not sure how early you can put on wing bands and don't know how many you'd want to put on one wing. You can get labeled bands but you'd need to handle them to read the labels. And you can get colors you can see without handling them. I could see a system where the color of the band on the left wing was the year they hatched where the color on the right wing had some other meaning so you could read that without catching them, but I'd think the total number of different colors would be limiting. Maybe a combination of colored and labeled wing bands?
There are variations in leg bands and these come with a risk. You can get labeled bands but you need to catch them to read them. You can get colored bands so you can set up a system where you can read them without catching them. Since you can put more than one band on a leg you can get a surprising number of combinations using colors. For example, use the left leg to identify year they were hatched or maybe a certain parentage, while a blue band on the right leg signifies one individual, a blue and yellow a different individual, or where a yellow band between two blues means another one. This is my method but instead of using bands I use colored zip ties. This works fairly well when they are walking around but does not work when they are on the nest laying eggs with their eggs tucked under them.
The risk in using bands or zip ties is that their legs grow. They may become tight enough to cut the foot off or seriously injure them. You have to check them. I prefer zip ties to the hard plastic bands because the hard bands come in certain sizes. You need different sizes of each color to match the leg size. The zip ties are adjustable when you first put them on. Neither of them stretch so you do need to check them, I want to emphasize that.
A temporary marking method is to use colors on feathers or down, often food dye or food coloring. A certain color on the head might mean one thing, a color on the right wing another, or a color on the left side of the abdomen might mean something different. Lots of options to store a lot of information. The problem is that it is temporary. The dye should color the down or feathers as long as they have them, though they might fade as the feather wears out. Not sure how the oil in duck in duck feathers will affect that but would not expect a problem. But they soon shed down and replace it with feathers. Chicken chicks go through juvenile molts, they outgrow their feathers so they molt and replace them. I'm assuming it is the same with ducks. So constant monitoring and touching up.
I have no idea which system or combination might suit you best. But I've tried to lay out options for you to explore. Good luck!
