Per Baseball America's transactions column. May was converted from shortstop to the outfield to catcher while with the Dodgers. He made several appearances on their top prospects list, twice reaching #17, and looked like a pretty good prospect after hitting .306 in 2009. His hitting fell off, though, after LA traded him to Kansas City for Scott Podsednik in July 2010. He collapsed at the plate in AAA with the Mets in 2012, posting a .593 OPS.
With Ramon Cabrera traded, the Pirates had only two catchers above the class A level who could be considered any kind of depth, those being Tony Sanchez and Ali Solis, so I was wondering when they'd sign somebody else. May has a lot more experience at AAA than Solis, so I imagine he'll share time at Indianapolis with Sanchez.