Symantec notifications when block application can disabled by client or by Symantec Endpoint Protection Manager.
Those few steps will show hot to disabled block applications notifications by Symantec Endpoint Protection Manager.

1. Open the Symantec Endpoint Protection manager console.
2. Login using user and password.
3. Select "policies" on the left pane.
4. Click "Firewall".
5. Double click "firewall policy" on the right pane.
6. Select "rules" on the left pane.
7. Click "notifications" on the right pane.
8. Uncheck "Display notification on the computer when the client blocks an application".