1 - I create a 3D text visible only to a specific player.
CreateDynamic3DTextLabel("Text here", 0xEEDD82FF, Pos[0], Pos[1], Pos[2], 4.0, INVALID_PLAYER_ID, vehicleid, 0, -1, -1, playerid, 4.0);
For another player who cannot see this text I use Streamer_ToggleAllItems(playerid, STREAMER_TYPE_3D_TEXT_LABEL, false); and then I use Streamer_ToggleAllItems(playerid, STREAMER_TYPE_3D_TEXT_LABEL, true);, so this player starts to see the text that he shouldn't see!