Great pics Jass!
MPA is Massachusetts Port Authority. They own alot of the land down there and for some reason they have jurisdiction over some of the streets.
Interesting tidbit: Massport has maintained ownership over its parcels in the area and entered into longterm leases with the developers rather than outright sale. The reason: proceeds from sold land go to the State's General Fund. Lease revenue stays with Massport.
So MPA = massport? I saw a lot of massport branded signs, so I guess MPA is just out of use?