At Cottonwood Cove, passing a Barter check of 35 with Aurelius of Phoenix gives you the opportunity to turn in dogtags for Caesar's Legion fame, and a reward of 10 caps each. Tags then can also be traded with Decanus Severus for ammunition and supplies, unless you are vilified by the Legion, in which case Severus may acknowledge you but will not trade.
Almost all NCR personnel carry dogtags prior to being killed. As they are weightless, they can be pickpocketed with little chance of failure.
Silent, hidden kills to NCR soldiers do not result in loss of Karma or reputation. However, if the target does not die immediately, they and any nearby fellow faction members will likely become hostile toward the player.
The tags are weightless and count as quest items, making them impossible to remove without console commands.
pcps3xbox360 Most troopers and named soldiers at Camp Forlorn Hope are set up to receive a set of dogtags when killed, this in addition to the dogtags most already carry, meaning corpses of Forlorn Hope personnel will frequently be found with two sets of dogtags. [verified]
pcps3xbox360 It is sometimes possible for known corpses carrying NCR dogtags to be found alive. This is an issue with the Gamebryo engine. If the player attempts to kill the non-player character who has been found alive, it will result in the usual Karma/reputation penalties as with killing any other non-player character. [verified]
pcxbox360 Skirmishes between the Legion and NCR soldiers between Camp Forlorn Hope and Nelson may not occur, forcing the player to look elsewhere for dogtags. [verified]