I'm not sure I even understand the question. Can you give me more context? What are you doing?
On its face, an announcement is usually disseminating information. For example, if I'm at dinner with my girlfriend and she stands up and says, "I have an announcement to make," the next words out of her mouth are probably going to be pretty important , like "I'm pregnant" or "I have cancer" or "I'm sleeping with your brother."
I suppose it could have a suggestion tied to it like, "Attention! We have a blood shortage here at the base and we need your help! Please give blood!"
Let me know if this helps at all. Peace!