A common assumption is that water is necessary for the existence of life. If that assumption is correct it is likely, assuming the other building blocks of life were present, that the presence of ice is indicative of life once existing on Mars. Life exists in many surprising places on earth. The ocean floor and thermal vents in the ocean are just to examples of life existing in extreme circumstances here. It seems that when the building blocks are available, life will find a way and there is no reason to believe that is not true for Mars.
Orbiting satellites, two hardy rovers, and a lander near the north pole have been sending back exciting evidence that the red planet may have once hosted oceans, rivers, and lakes of liquid water. there is a compelling evidence for the planet's watery history—including hints that life may still be lurking below the surface.
No, the discovery of a large reservoir of ice on Mars does not prove that life once existed on the Red Planet, but it does show that we may be able to live there some day. Where there is water, there is life. This does not mean there has been life, but there can be in the future.
It is not necessarily the case that life existed on Mars just because water was once present on the planet. However, it is the case that it opens up the possibility that Mars could have been the home of life forms at some point in the past. Once scientists are able to analyse samples properly they will be able to make a definitive judgement.