Just a guess, but the piece of steel may be a remaining support for a height-restriction beam that was once in place. Again, just a guess--can't verify that, unfortunately.
No idea what the steel on the top chord is.
As for Massillon, here is my info:
Massillon Bridge Company 1869-1930s
Toledo-Massillon Bridge Company, reorganized, c1905
Massillon Bridge and Structural Company, 1909 became a division of Fort Pitt Bridge Works in 1930s
Didnt Massillon Bridge Company go out of business in 1901? I thought I read that somewhere
I had the same thought when I saw the outline of the plate. I had just left the Stancer bridge before hitting this one.
The piece of steel on the one top cord really has me wondering.
Its not the least bit surprising this is a Massillon. The other pinned truss in the county is also a Massillon, same plaque type. Michigan historic bridge inventory gave a c. 1910 date. Both this and the 1900 date are incorrect. It likely dates to around the 1888 date of the other bridge which is Stancer Road. http://www.historicbridges.org/truss/stancer/index.htm
I was able to determine from the outline shape of the missing plaque that this is a Massillon product.
The 1900 date is probably a default date with this bridge likely being from the 1880's
Closed to traffic
I was reviewing my recordation of the bridge over at HistoricBridges.org and now that I look at the beam I believe it was put there to hold a "No Fishing" sign. There were No Parking signs all over the place leading up to this bridge. I believe the county had trouble with people hanging out and fishing off the bridge, and they probably put some sort of No Fishing sign up. You can see the bolt holes and perhaps the outline of a sign in my photo here: http://www.historicbridges.org/truss/gower/smich210.JPG