The sticker is normally located on the throat of the throttle body, and is usually covered up by the air duct coming from the air cleaner housing. When you loosen the clamp and remove the hose, it should become visible.
Now, for the rest of the story as told to me at Ford training school back in '91:
Due to buildups behind the throttle plate, driveability was affected. This resulted in irregular idle, stalling, hesitations, and surging while driving. Frequent cleaning was becoming necessary to keep cars running properly. Engineering went to work on the problem. The solution they found was to add a calibrated orfice toward the center of the throttle plate and to seal the edges. This made the buildup behind the throttle plate irrelevant, since it could no longer affect the airflow. A special coating was used to seal off the edges of the throttle plate at closed throttle. Removing or damaging this coating frequently resulted in erratic idling that could only be remedied by replacing the throttle body.
Now, since there are always manufacturing variables, sometimes there are no immediate ill effects from cleaning. Sometimes there are. Since replacement throttle bodies are expensive, I choose not to take chances and upset things by ignoring warning stickers.