I think this is also applicable to Microsoft Access:
In Visual Basic version 4.0, the exclamation mark (!) syntax is for collection lookup, and the dot (.) syntax is for properties and methods.
However, a control can be accessed as a property, and Visual Basic has a Controls collection on a form. Because the Controls collection is the default property of a form, you can access a control from a Form using by using the exclamation mark (!) syntax.
(source:http://support.microsoft.com/kb/129287)
In a formula, it indicates that external data is being brought into the formula of function.
A triangle with an exclamation point is the usual symbol on Microsoft Windows systems for an "exclamation" event. This typically indicates a system event notification that can be an error or needs human intervention.
What does the triangle with exclamation point light mean in 2006 Lexus Gs 300
If the exclamation point is inside a yellow horseshoe, the tire pressure is low
Usually, " warning!!!"
The yellow exclamation point light on a Honda Accord is designed for the Vehicle Stability Assist system. It comes on when the vehicle is trying to maintain stability or when a tire is low.
Tire pressure.
It means you have an idea
Caution or warning
you have to put air in your tires. That's what the exclamation point signifies
Tire pressure
it means that the handbrake is on
TRACTION