More empty weapons racks early in Cairo Station. These resemble the automatic one from the Halo 2 announcement trailer, but do not appear to animate in any way. I've emptied the rack all except for one SMG that wouldn't let me pick it up, and carried them down to the loading zone past Commons and before Hangar 01.

And here is the tragedy at last: after you go up the stairs and get the checkpoint, all the lovely guns from the early areas get garbage collected. The only ones remaining are the Covenant weapons picked up and the human weapons dropped during the two battles. The ones taken from the racks have been removed.

And here they all are: all the human weapons from the weapons racks earlier in the level, and most of the Covenant weapons from the battles up to and including the one in Commons, before Hangar 01. Once you go up the stairwell to the left of this area, the door to Commons locks, so I knew I had to drop the weapons on this side of the door...

When Cairo Station begins, this crate is covered with weapons. I've carried the ordnance to the loading zone beyond Commons.

On the landing above the area where the Covenant break in there are two automatic weapons racks holding SMGs and Battle Rifles. I've emptied them and carried the ordnance to the loading zone beyond Commons.

At the very opening of Cairo Station, just down the stairs towards where the other Marines are, there are two different kinds of weapons racks. I've emptied them and carried the ordnance to the loading zone beyond Commons.

A poster on the Bungie.net bulletin board named EschewObfuscatio says he found this symbol on a piece of wreckage from a destroyed Wraith. It's unknown as yet if this is his rendering of the symbol or an actual portion of a screenshot or video capture. It looks very much it could be part of a new glyph puzzle.