From:
Unmanned Aircraft Systems (UAS) Frequently Asked Questions
I'm a foreign national and want to fly my UAS in the U.S. on vacation. Do I have to register before flying?
If you are a foreign national and you are not eligible to register your sUAS in the United States there are two ways for you to operate. If you want to operate your UAS exclusively as model aircraft you must complete the steps in the web-based registration process and obtain a "recognition of ownership." This recognition of ownership is required by the Department of Transportation to operate a model aircraft in the United States. Alternatively, if you want to operate your UAS as a non-model aircraft you must register your UAS in the country in which you are eligible to register and obtain operating authority from the Department of Transportation.
NOTE: at this time, the FAA's online registration website can only be accessed from a computer located in the United States or its territories or possessions.