I don't see any prohibitions on pictures attached to your account. I do see the image links you did place in your sig to be potential problems. They are links to Myspace-hosted pictures and it is quite possible that Myspace prevents hotlinking of images (what you're trying to do). I suggest uploading the images to Imageshack and then putting them in your signature. See instructions in a previous post of mine.
I think you're going to need to resize those. We don't have a strict size limit but those are way too big. A good one to size yourself against in terms of height and width might be the Danimal's. Example here.
Although photobucket can be a pain in the ass sometime, it does have a helpful editing page for re-sizing pics, and now it has some crafty type crud that you can add to manipulate a photo.