This bird was found and photographed on May 27, 2015 on the bayside shoreline north of the bridge approximately at the north end of the main parking lot. (42.051739, -70.645866)....
This series of photos shows the flag from several angles - none of which reveal any lettering. They also show some sort of white ring/metal band on the left leg.

It was basically by itself though there were a couple of Sanderlings, a Turnstone and 2 other SESAs nearby.

Jeaninne Parvin from bandedbirds.org (an awesome group/site!) reports the following:....This bird was definitely banded in Brazil. Metal band on upper left and Engraved Dark Blue Flag on upper right (no geo). Sorry to see this ink did not hold up! The location of the study site is: Coroa dos Ovos, Maranhao, Brazil -1.447344 -45.161111. .... The research project has had an expedition during austral summer since January 2012. .... The researchers are David Mizrahi of New Jersey Audubon along with collaborators in Brazil.