If there were water or ice on Mars, it would reveal itself the same way water and ice on Earth does when observed from orbit, by brilliantly reflecting the sun at certain angles. I don't have a good example of this in a postable photo, but I have seen shots taken from the Shuttle where small ponds, rivers and lakes glow brilliantly against the background of the Earth's surface. Frozen water does the same thing, although not as brightly. This effect is particularly noticable in movies, where the sun's reflection moves along the Earth's surface, highlighting the smooth surfaces.

Now on Mars, any liquid open water (unlikely, IMO), or smooth ice surface would also do this. It would be simple to calculate where the orbiter would have to be to catch the sun's "glint" off a suspected water/ice surface. Far more difficult would be trying to figure out how to get the orbiter to that exact position at the right time.

It would be much more likely that such a glint would be caught by accident, like the first Io eruptions. Given the operational parameters of the Mars Global Surveyor, this might not be likely even if there were many "puddles" on Mars. For the typical Mars Global Surveyor photo, taken more or less straight down, the sun would have to be almost behind the orbiter to catch a reflection. Typically, scientists try to "shoot" terrain when the sun is off local vertical a good distance to get much better shadows and definition of surface features. Shots of rocky planets like the Moon or Mars tend to look quite bland when the sun is directly behind the camera. Still, a heads-up to scientists to examine photos that, for one reason or another, are taken under ideal reflecting circumstances, to see if there is a "glint."

Of course, it's not as easy as that. Polished rock or lava surfaces can also "glint," but typically lakes and such make much larger reflections.

Also, with the constant dusty environment, any surface ice might be covered with dust quite quickly, and would no longer reflect. It would not take a very thick dust coating to drastically reduce the reflectivity of an ice surface.