What you saw was probably the old granite "curb stones" that lined the platform edge at Lake St. At Linwood Place there's an old gong style crossing bell, and in Arlington Center, the signals that guarded the Mass Ave intersection are still in place. Past Arlington Center are a few cement whistle (W) and "R" posts. Before grove street on the high school side of the ROW, and behind the DPW buildings is the remains of a coal trestle. At Brattle Street there is a rusting diamond shaped sign with "OB" in large letters. This sits at the south end of what was once the Brattles platform. Between Brattle Street and the Skating Rink you can see the remains of a siding that split off the left and descended to the parking lot. This was once met with an 18" or 24" cart railway, but those tracks were paved over about 5 or 6 years ago. Between Forest St and Lowell St there's an old "Stop Look & Listen" sign made out of a spare piece of rail. Between Lowell St and Park Ave are two sidings, though one is mostly paved over. You can still see the frog showing through the pavement. Until about 5 years ago there was a tell-tale attached to the side of Gold's Gym to warn crew members on the car of the clearance issue where the trackage entered that building. There also appears to be a concrete tie (why, I don't know) discarded behind the old-folks-home/walgreens. I'm not as familiar with Lexington, but there are two sidings between Lexington and the Bedford line, and some rail discarded around the Hartwell Avenue crossing.
Did we ever hear a music sweeter than the one that thrills, as it floats along the Deerfield, as it echoes o'er the hills.
How we watch that little engine as it stalks across the plain; was there ever music sweeter, was there ever sight completer, than the coming of the train?
-E. A. Fitch