The BattleField 3 knowledgebase says:
Will veteran ranks and status earned in previous BF games grant bonuses in Battlefield 3? Yes, you will have unlocked a silenced M1911 pistol. Also you will receive dog tags associated with previous games if you registered those games.
I have Battlefield 1942 (all expansions), Battlefield 2, Battlefield 2142 and an accout on Battlefield Play4Free - so how do I "register these games"? Do I have to put the CD key into Origin or something else? Is it even possible to get the tags after so long?