Oahu's "Diamond Head" is quite noticeable, very interesting place. You can see it all along Waikiki beach and beyond. Old paintings always depicts early islanders at sea with Diamond Head in the back drop. Guam's "Two Lover's Leap" kind of looks like a slide going into the water but the slide is totally vertical. I could see this feature at sea all the time and you can see it in Tumon Bay and from even the airport. Rota's "Wedding cake mountain" is another feature on this island that sticks out like a sore thumb. It's distinguishing shape gets it that name obviously, and pilots know all about wedding cake mountain.

Anyone know of any good distinguishing natural landmarks?

Here is a great view of Diamond Head....

diamond head - Bing Images

View of two lovers leap from the sea. two lovers leap - Bing Images

Wedding cake mountain

wedding cake mountain rota - Bing Images