Early warning system (solar radiation)
Like Earth, Mars has its own Lagrangian points with the Sun. Currently there are no man-made satellites in or orbit, but it is conceivable that these islands of gravitational stability may be used to greatly benefit future Mars colonies.
Early warning system for the onset of solar storms
Instruments in the Earth-Sun point already provide scientists on Earth with an early warning system to monitor space weather. Probes such as SoHO and ACE receive solar ions approximately an hour before they impact the Earth's atmosphere. This not only provides excellent diagnostic data, but also gives advanced warning to companies and organizations that the Earth is 60 minutes away from experiencing an increase in solar radiation. Emergency procedures can be enacted accordingly, possibly saving delicate satellites and astronauts.
A simple, cost effective probe may be inserted into the Mars-Sun point. This probe needn't be as sophisticated as SoHO or ACE, it just needs to monitor the flux of energetic particles travelling toward Mars. Akin to a "flag" system on a patrolled beach (red for "dangerous", no swimming. Green for "safe", water is safe), Mars settlers could have advanced warning of an incoming CME from the Sun. If constantly measured by a particle detector on the probe at the point, various stages of danger levels may be used to indicate to settlers unprotected on the surface of what severity of risk they are in. Surface "walkabouts" may be tightly restricted by such a system.