There have been paintings (yes, I actually have painted) where I spent hours fretting over where to put the signature.
I hate signature angst. It's right up there with dentist appointments or other life dreads. The best way I settled on was to subdue it by using a paint color only slightly different in hue, saturation or intensity from the spot where you are placing the signature.
I tried to make my signature a design element once, but a potential buyer just did not see it that way. Not famous enough, I guess. Famous people probably can get away with garish signatures, but us peons have to hide them.