first i would like to tell ajit that the machine does not require a restart for the policy being applied to clients, it will automatically get the new policy as the time is mentioned in the server of how the clients will check for policy updates.
Secondly Sam you can try looking into 2 things
a) In the application control policy if you edit an existing application control policy u will find an enable logging checkbox in the top right hand conrner of the screen, youcan uncheck that and see if the notification stops or not.
b) In the device control policy setting you will see a notification area at the bottom of the screen saying that "Notify users when devices are blocked" chek that if the check box is checked there or not. uncheck it and i think your problem will be solved.