okay!
before I start I just want to mention that some people (myself included) have shops in the museum shop section of the forums where you can buy custom made signatures ^^
that said,
- first of all the maximum size for signatures allowed on the forums is 715x250 pixels. You don't have to have one thig big (most people don't), and keep in mind that if you want to add written text under your signature, the image itself will have to be less than 250px high.
- I don't use brushes on my signatures, instead I use shapes that I find mostly on google images or deviantart. sometimes they're regular like a circle or rectangle or such, for most custom ones I would type something like "flower silhouette", and use a transparent image as a base for my signature. Over this I would add a layer with a background (clipping the layer) and then add text, villagers, etc.
(part 1/2)