You can use Photoshop, GIMP, or even Paint. There are some villager pixels on tumblr and you just put them on the background you want and add text. I think that even most people who make signatures for free or in exchange for TBT use backgrounds that are pre-made so you can search for some you like and use them.
I could make you one but I've temporarily uninstalled Photoshop. There are people here on the forum who take requests or TBT commissions, though.
