There was a lot of back and forth on the 3D MPD listserv back in September 2007 about a shooting that had occurred near 508 M St NW. There is a photo of a bullet hole that pierced a window at the address.
Looking at the DC PIVS, the building was at one time condemned and had been vacant up until 2011. Between 2009-2011 there were permits issued. The DC Tax database for the address looks, weird. The entry for 0482 0071, 508 M St NW is in the name of International Group LLC, the owners mentioned back in 2007. They have not paid any taxes since 2009, but have been credited after that and currently have a negative balance. Maybe the unit was broken up into condos? It is several units as there are a few different electrical meters. however a look at the block reveals, no other 508 M Streets NW unit anything.
This is the DC Vacant Properties blog, not the DC Property Tax Watchdog blog, so the only thing I'm going to say is this is occupied.