I did some magnifying on one of the wallpapers for odst and guess what I saw in the reflection of their visors. Master Chief. It just looks like his helmet looking up, so maybe (possible spoiler) when you regroup with all of your team you see the chief. Maybe. The link http://www.bungie.net/projects/odst/asset_popup_viewer.aspx?a t=60&cc=29&item=0 if you want to see it. Just look in Rookie's viser on the right it looks like master chief, or it could just be another ODST that they are looking at or just a burning building. Now I looked on youtube and the bungie.net and I couldn't find this any where so I guess I'm the first.
[Edited on 08.07.2009 2:52 PM PDT]