Billboard Senate Blues

The Washington Post reports on Senator Reid's protection of billboards, which he says is "a matter of personal importance":

In a (quite) large sign that protecting U.S. troops isn't the only thing on Senate Majority Leader Harry Reid's mind these days, the Nevada Democrat inserted an item into the Senate's Iraq war funding bill -- safeguarding billboards.

Senate debate began yesterday on the bill, which provides $122 billion for the wars in Iraq and Afghanistan; sets a goal of March 31, 2008, for withdrawing U.S. troops from Iraq; and -- if Reid has his way -- allows thousands of billboards destroyed by bad weather to be rebuilt.

An opponent of Reid's measure is quoted in the news article:

Kevin Fry, president of Scenic America, said: "The bill carves out an exception to local land-use rules for a single industry that is not available to any other. . . . One might reasonably ask why legislation affecting the South and Southeast was introduced by a senator from Nevada."

Is it also just too much to ask that the Senate majority leader, and every member of Congress for that matter, consult the Constitution? It seems to me that the Supreme Court's constitutional jurisprudence has taken local land use rules to be a matter of police power, which is supposedly reserved by the 10th Amendment for state government. Constitutionally speaking, Congress is supposed to have certain enumerated powers which are located in Article I, Section 8. I can't find the police power there, nor can I find any other power in the list of enumerated powers that I think sounds like specifying rules for billboards.

Is there something I'm missing?