There is a 700 pixel maximum width for images posted on the forum and a 250 pixel height maximum for signatures as per here.
If you have an image you wish to post that is wider than 700 pixels, you can use the [imgw] tag to post it which will restrict it to this width and automatically scale the height accordingly, which I have done for you. Can you please alter your signature to how you see fit to ensure it is no higher than 250 pixels.