I make them with Photoshop CS5, but I've heard of others using GIMP (which is free)
They get the images of the dreamies online~
Hope that helps! (▰˘◡˘▰)
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.
If you'd like Nyan, I could make you a pixellated animated one like the ones you see on here for free
I'd like the practice, so PM me if you'd want one! (✿◠‿◠)
I'd give you all the info there~