What you can do is try rubbing it with increasingly more abrasive things, to see if it comes off.
First thing I try is my fingernails, if that doesn't work, I try those green Scotch-Brite pads (the thingies you use for the dishes). Then I scraped it lightly with a flathead screwdriver (this did it for me). If that doesn't work, I guess you should go to steel wool or a polishing compound like Brasso, Flitz, or Mothers Mag & Aluminum polish. These will probably put a bright spot on the finish, but who the heck cares-- it's a Strider!
I've had rust spots form on my Strider too, around the handle area. Since I carry it on my belt under my shirt, it's probably the sweat. Now I coat the handle with Tuf-Glide every once in a while.