May 19, 2015
On Tuesday, May 19, 2015, the President signed into law:
S. 665, the "Rafael Ramos and Wenjian Liu National Blue Alert Act of 2015," which requires the Department of Justice to establish a national Blue Alert communications network to disseminate information on: the serious injury or death of a law enforcement officer in the line of duty; an officer who is missing in connection with the officer's official duties; or an imminent and credible threat that an individual intends to cause the serious injury or death of a law enforcement officer.
Barack Obama, Statement by the Press Secretary on S. 665 Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/319541