"Entering battle" indicator

What is this suggestion related to (eg. Website / Launcher / The game itself / etc. ): Battle start indicators

Description: At this moment there is no way to notice that you have engaged a hostile NPC, other than to see that.
Add some sort of indicators which indicates when the player enter the battle with NPC. The moment when the player triggers NPC(makes it start to perform any actions to the player(running, casting, self-casting, shooting).
Usually the “hostile npc performs any actions to the player” indicators are:

1. Red contour at the player nameplate.
The contour appears at the very start and lasts till the battle ends(death or any other ways to end the battle). Also can be used on enemy name plate in case there are several enemies and the player need to know which one is focused on the player.
2. Sound.
Usually at the start of the “hostile NPC performs any actions to the player” action some sort of sound appears. Which indicates the start of the battle. Something like that Impact, hollow plastic, large 1 - ZapSplat - Download free sound effects This sounds is need to notify the player about NPC is taking a fight with the player, in cases when NPC can not be seen at the engage exact moment(from behind, for instance).
If start battle sound will make it to the game i would advice to do some sort of a poll to see what people think about different start battle sounds.
3. NPC focus switching sound.
NPC focus switching from one player to another should end up with sound effect. The player should know if merman who is being tanked by another player(no matter are we party up or not) switches its focus. This sound can be used only if the battle is already happening otherwise use “hostile npc performs any actions to the player” start sound.
4. Text.
Text notification just like that
There are many ways that the aggro text could be done. Pretty hard to name that one which going to be the best one.

Those effects usually come together. Usually the contour comes with the sound and sometimes with the text.
Its pretty hard to advice the only way it should be done, if those changes are going to be ever implemented. I would advice to do some sort of testing to get players feed back.