I largely like to annouce my attack in some way shape or form. The reasons for that are I like to hear what people say before they feel the heat of my laser blasts. Also, it is generally considered a decent thing to do (realism aside for a second here) as I have been thoroughly annoyed when apparently neutral IFF'd ships have blown me up while I am sat still without a word said.
There are occasions wher you are maintaining radio silence and therefore you don't say anything, however in situations like that it is pretty clear cut before a shot is fire who you are.