200 pixels in height is extraordinarily cramped if you want to have even just two images in a sig.
570 width for images is pretty weird if the posts in the forum have about 50 pixels more horizontal space than that, and long images like banners at the top of threads get squished if they go over that limit.
I'm complaining about ZB width limits in general here, I know you can't change it.
The point is that when you compare the limit to other forums, it's not small at all. It's surprising that somebody would be surprised about the sig limit.
(and especially considering it's been 200 for three years)