Legal citation is full of legal abbreviations.  A number of these are easily recognized by legal researchers (P.2d, F.Supp, U.S., etc); however, many others are completely foreign (A.N., EWiR, W.L.R.,).  You'll probably encounter some unfamiliar abbreviations when performing a source pull or reading a law review article.  When I'm looking for the meaning of a legal abbreviation there are two places I turn - Prince's Bieber Dictionary of Legal Abbreviations and Cardiff Index to Legal Abbreviations. 

Prince's Bieber Dictionary, or Bieber's as many librarians call it, focuses on abbreviations and acronyms found in American legal literature.  It is a book found behind the law library reference desk (KF 246 .B46 2009) in which you can look things up by abbreviation or by title.  I have cracked the code of many unfamiliar abbreviations with Bieber's as my tool. 

Cardiff Index to Legal Abbreviations is a web-based tool that focuses more on foreign and international legal abbreviations than does Bieber's.  Freely available on the web, this index's search functions allow you to search by both abbreviation and title.  Its foreign and international abbreviations make it an excellent companion to Bieber's.

With these two tools you're unlikely to get stumped by a perplexing legal abbreviation.