Brotherhood of Steel holotag (Fallout 3)

Every member of the Brotherhood of Steel, just like soldiers of the US Army they are descended from, wears a set of two Holotags around their neck. They contain essential personal and medical information about the wearer.

Unmarked quest: Collecting Holotags
In Fallout 3, holotags recovered from fallen Brotherhood members can be turned in to Scribe Jameson at the Citadel (A-Ring Archives) in exchange for 100 caps and 25 XP each, but only BEFORE embarking on the Take it Back! quest.

Locations

 * A-Ring, in the Citadel, has one in the Den on the small desk just before the room with the beds.
 * The Mall has two. There are two dead Brotherhood of Steel initiates there, one on sandbags right in front of the Super Mutant Bunker door, other inside the mentioned Bunker, next to a table. (NOTE: I found 3 BoS Initiates here. One in the bunker, one just outside it, and a third one at the south/north end (can't remember, sorry) of the trench network. Just explore all the trenches and you'll find the poor bugger).
 * Falls Church is another location that usually has one or two. Upon reaching the location, there will be a big fight going on between Brotherhood of Steel members and Super Mutants. They will not be able to kill all of the enemies. Every corpse from a Brotherhood member will have a holotag.
 * Note: try to keep Paladin Hoss alive. He's essential to a minor side-quest on Falls church.
 * Olney Sewers, there is a holotag on the dead Brotherhood Initiate with the Prototype Medic Power Armor.
 * Arlington Library - several Paladins will attempt to clear the library of Raiders when the player arrives. If any fall, their tags can be collected.
 * Galaxy News Radio usually has around 3 knights with holotags. If you wish to be evil you can kill them or wait for the super mutants to respawn and kill them.