The rule violation occurred during last Friday night's Busch Series race at Richmond International Speedway.
Truex lost 25 driver championship points and was fined $10,000 for the gesture. He was put on probation for his actions until Dec. 31, 2005.
Teresa Earnhardt, Truex's car owner, also was penalized 25 owner points.
"I would like to apologize for my actions during last week's event at Richmond International Raceway," Truex said. "All of the employees at Dale Earnhardt Inc. and Chance 2 Motorsports work very hard to earn every point available and I let them down.
"My emotions got the best of me and I did something that is very much out of character," Truex added.
Truex now leads the championship standings by 69 points with seven races left.