If on skis, make an X with them on the top. Never just ride by someone in this situation; as riders and skiers, we all should look out for one another just a little bit. Not only could you be saving someone`s life, but it might be your ass on the line someday and a little good Karma might come in handy!
QFT! i had a bad fall, broke some bones, and no matter how hard I tried, I couldn't unstrap or stand up, I was just stuck in the middle of a run. several people rode past without even looking my way. finally someone helped me unstrap and I was able to stand up barely and flag down a patrol on ski mobile. Now I always pay extra attention to others that have fallen, and have helped out a few.