There is no "HIDE" packet. It's done purely client sidedly and can't really be done via Packets. At least not naturally... You COULD technically do it by packet based despawn of the unique and re-spawning it using the same MobObjectID with a "invisible" model. That WOULD have the same effect, but you'd have to handle Singlespawn, single de-spawn, group spawn, group despawn for every single character.
Additionally, to get the "TARGET" icon... just get edxloader, start up the sniffer and just login 2 chars.
Select both chars, and get 0x7045 to find the CharObjectID. Then spawn the unique and let it target one of the chars. Get all the packets after spawn until target.
CTRL + F for the CharObjectID and you'll have at least 1 hit. If you have multiples, just find out what the opcodes are for.. If you can't.. login to a vsro 188 server and get all the packets as well and check which packet is "new" since vsro 188 doesn't have that icon.
Should be pretty easy though.