Center

This is one I made. I found an arrow outline, duplicated it and arranged it in the various directions. The circle was made from scratch, which is easy in an image editor. Then I combined them, textured them, and added a black glow to make it pop from the background. Since the arrows radiate out in the same directions as the ribs of the porthole, I broke my own rule about the image being "outside" it and laid it atop the ribs. Otherwise, you wouldn't be able to see the arrows.