I'm guessing you mean graphics? I would maybe check out a shop. There are people who will sometimes do it for free or charge a small TBT fee.
They usually tend to use Photoshop or other software meant for making graphics and such.
It's really not an easy thing to do, and Photoshop is not cheap at all. Gimp is a free software meant to work like photoshop, but I dont like it personally.
You could download it and give it a try, but it's something that will absolutely not happen over night. You really just have to teach yourself. Which can take a long time.
I used gimp for mine, but I made the mistake of not saving right before I put my villagers on, or I made the mistake of overwriting the save after putting the animation (I don't remember which one it is.), now villagers moved in and I can't add them without starting over, and my sig would probably be different. It's ok after you get the hang of it. If you are using gimp and want to know how to do something, there are probably guides on how to do it, on the internet (where you can now find everything). And I messed up one villager (I didn't put the right one, oh well.)
Also, if you see someone's sig that looks really good to you...ask them who did it for them. That's how I got mine. I saw someone's sig, and it actually said the name of the person who made it. So I contacted them and asked them to make mine. Even though they didn't ask me for any TBT, I still chose to give them some, to be fair and all. ;D