Here are some "worked examples" of URN:lex identifiers, to act as a guide for those implementing URN:lex on their sites. Discussion of this topic is taking place here.
United States Code (per the Legal Information Institute):
For now, we are implementing US Code URNs inside <meta> tags, along the lines of the following example:
URN:lex is a proposed Internet standard for legal document identifiers written by Pierluigi Spinosa, Enrico Francesconi, and Caterina Lupo. It is intended to coexist with (and provide important infrastructure for) more semantically-laden approaches like LegisLink and Citability.
The law.gov workshop held by the Legal Information Institute at the Cornell Law School on March 22 and 23, 2010, produced some general recommendations regarding legislative metadata. They are best imagined as a series of answers to a question from a revisor of statutes or other governmental publisher of statutes or regulations who is asking, "What should I do?".