USPTO has confirmed that on October 2, 2013, the United States has signed the Marrakesh Treaty to Facilitate Access to Published Works for Persons Who Are Blind, Visually Impaired, or Otherwise Print Disabled. The U.S. signing, which was not accompanied by a press release, took place on the last day of the WIPO General Assembly, and one day after the United States government began to shut down non-essential operations as a consequence of disputes over the Affordable Care Act.
As reported by WIPO, the number of countries signing the Marrakesh treaty is now 57.
I would have expected more signatures from countries where English is widely used, but this may come later, particularly since the UK and the United States have both signed. The signature by the United States may have an immediate impact on the perception that exports of accessible works are allowed under U.S. fair use exceptions.