Messages on Bomb
From Halopedia, the Halo Wiki
When you drop the assault bomb on any assault game of Halo 2 Multi-player, there is a hidden message that you can see as it falls. These are visible in The Art of Halo.
The best way to see it is to perform the No Weapon glitch and pick up the bomb, walk to a wall and hold R so the bomb is quickly bouncing between you and the wall. If this doesn't work because the wall is too light/the bomb is too much to one side of the screen then look directly up and hold R and you can see it as its thrown into the air. Also, it helps to be a Spartan as it is much easier than being an Elite because the dropping animation is different.
This difference means that the bomb drops directly down, not forward first.
An alternate method is to simply grab the bomb and to drop it into a shiny area of the map, and then zooming at the bottom of the bomb with a Sniper/Beam rifle. The message can easily be read that way.
[edit] Messages
The messages seem to correspond to what map is used.
For instance, the message 'Thus I Refute Thee' appears on Ivory Tower, Waterworks, Turf, Backwash, Elongation, Relic. On Bungie.net's matchmaking stats section of the service record, the description of the bomb is "Thus I refute thee."
'Hold Onto Yer Butt' appears on Ascension, Burial Mounds, Warlock, Gemini.
'Kiss It Goodbye' on Coagulation, Headlong, Sanctuary, Terminal and on Tombstone as well.
Hieroglyph of a Spartan helmet, the two fingered peace symbol then xoxo ♥ appears on Lockout, Midship, Beaver Creek, Colossus, Zanzibar, Foundation, Containment and on Desolation.
