Help exclamation mark

[Halfpint]

I understand that the red exclamation mark behind sent texts has to do with a setting. Can I get someone to guide me thru on how to change this. I went to menu then settings on my HTC hero but didn't see anything that stood out to me.

 

[ghostlyease]

I was led to believe the exclamation mark appears on texts sending to people who have their messaging set to high priority.