Driving anywhere with skis on the car, I have to compulsively lean over the steering wheel and look up to see if they are still there. I know that if they were to blow off or something, I'd know about it (crash..scrape...shatter...). I'm a freak about it, though. In the 28 miles from my house to the local hill, I'll check 5 or 6 times without even realizing it. My friend started to make fun of me about it, but then he told me he does the same thing, only he has a sunroof he can just look up through.
I do this with my bike too. I angle my rearview mirror so that I can atleast see the pedal or back tire. I also watch the shadows as I drive to see if it is still there.
It's like, I'm afraid someone or something is going to climb on top of my car at 80mph and steal my shit. Like that gremlin thing on that Twilight Zone episode that was standing on the wing of the plane smiling at the dude inside.