HI,
Just bought a 2005 300, and have had nothing but trouble. I have a light on on the dash,, on the right hand side of the tach...that is a circle, in brackets with an exclamation mark inside. At first I thought it was a tire pressure sensor...but according to the owners manual, that is on the other side of the speedo. Driving me crazy..any info would be great.

 

it may not be a sensor it is usually u need to air air into one of the 5 tires.

 

That light is a brake warning light. You have an owners manual, it is described in there. The "brackets" are an icon representing brake shoes (more like a railroad brake than a car brake).
Anyway, it comes on if the brake fluid is low or if the system senses a failure of one side of the brake system. Either way, the "!" in the middle is trying to tell you that this is important and needs to be fixed yesterday.
This is a dangerous situation and you must get it taken care of.