I stumbled upon a USA Today article about tire pressure monitoring systems (TPMS). It had a large picture of a symbol I'm used to seeing in the tire industry, but it seems the consumer is far less aware of its meaning. The article goes on to reveal that Shrader (a large manufacture of TPMS systems) did a study that found a third of drivers didn't know what it meant. Even further, while people may know what the symbol means 46% of the group didn't know it was supposed to be a picture of a flat tire.
Basically, this symbol is going to come on via your TPMS if the tire pressure drops 25%. That is a significant drop that needs to be addressed.
TPMS is not meant to replace checking your tire pressure or carrying a tire pressure gauge in your glove box, but is obviously useful in avoiding a dangerous situation and could save you some money in the process. Not only can tires low on pressure negatively affect fuel mileage, but if you get a slow leak and keep driving to your destination your tires could have excessive deflection. As the tire flexes more than normal, heat and friction build up and can ruin a tire that could have otherwise been fixed.
Read your manual and know what the symbols mean because the warning lights sometimes aren't so clear.
For more information on TPMS read Tire Pressure Monitoring Systems and TPMS Servicing in our Tech Center.