The rules that use the category "<call_sign_controller>" are:

<controller-air_traffic_control-recursive>

<call_sign_controller> <digit> <digit>

<controller-air_traffic_control>

<call_sign_controller> <digit> <digit>

<controller>

<call_sign_controller> <digit> <digit>

<controller-recursive>

<call_sign_controller> <digit> <digit>