Go back to the two pictures posted by Bob. Compare the letter C in Texaco. The dead give away right there. The fakes have a letter C that is curved all the way around at the top and bottom. ( think a letter O with a chunk cut out of the side) The original has a Letter C that does not curve all the way around at the top[ and bottom.
Other fake signs can also be spotted this way with the letters C,G and S
That letter style is known as Helvetica and was not developed until the late fifties. Even so it didn't get much use til the sixties and became widely used around the mid seventies when there was a lot of architectural signage being used. It seems that everything was being done in dark bronze and white.
I hope all that makes sense.

ROD [Mich.]