Warren-You're correct, that is the Union Railroad emblem. Is it possible that you could provide us with dimensions of the piece, including the thickness of the steel? That might be a clue as to whether this came from a steam locomotive tender.
I don't know how much you've researched on the Union Railroad but here's a brief history on the Union Railroad at "Trainweb":
http://www.trainweb.org/pt/union.html
The current operator of the Union is Transtar, a little more on the Union RR here:
http://www.tstarinc.com
The Union Railroad rostered some unique steam locomotives of the 0-10-2 wheel arrangement. One of them still survives today, on display in Greenville, PA. However, it is painted for the Duluth, Missabe & Iron Range Railroad. I'm unsure when the Union diselized but some of their remaining steamers went to the DM&IR, as both railroads were at one time owned by the US Steel Corporation, along with the Bessemer and Lake Erie. I know very little about the Union RR so am unsure what other steam locomotives were on their roster. I tried the trusty Google search but came up with very little.
Photos here:
http://www.members.tripod.com/~greenville/rrpark.html
At your suggestion, I will move this topic to the "Pennsylvania Railfan" forum where it will most likely receive more exposure.