Its implied logically when we consider what the announcement system is. It can only be used by four things.
1. A head of staff ID using a communications console
2. The artificial intelligence using a special verb they have to create an announcement
3. Central command or CCIA using their own special verbs to send station announcements.
4. A traitor item used to create one announcement.
Now obviously we do not know about the 4th one IC. We only know about the first three. Your character is not a head of staff, is not an AI and is certainly not a central command agent. Thus we can deduce from this that you somehow gained access to the announcement system illegally. Thus we can further deduce that a search of your person was warranted.