Malvern –
It’s nice to see others have noticed the minute details that evolved from set to set in these signs.
I hope no one minds if I link to a couple more photos to illustrate the differences in signs, including some of what Malvern mentioned:
http://www.flickr.com/photos/elze68_sep ... hotostream
Additional small things like the tail piece of the "R" itself show how the fonts were adjusted, even just in helvetica.
Also, you can distinguish the age of the R style signs from their side markings that identify the routes. The very original ones used upper and lower case lettering, as well as marking the R on both sides, i.e. R6 Ivy Ridge - R6 Norristown, vs newer signs that are written in all caps and say R6 CYNWYD - NORRISTOWN, without the second R6 noted. It appears this may have changed when the commuter tunnel was opened, as the older signs have a MUCH greater frequency of varying sides (i.e. R1 West Trenton/R3 Elwyn, R3 Secane/North Broad, R5 Bryn Mawr/Suburban Station, R2 Baldwin/R3 West Trenton, and so forth). The newer sets eliminated all of these mismatched destinations, but I could be way off base with the tunnel reference - perhaps it was just done for cost efficiency?
Finally, in reference to the much more solid signs that you could really do some damage with: these were likely made on a large sheet and cut to individual boards, much like our paper currency is produced. For anyone who has these older signs, you can look around the borders to see if there is bleeding from other colors (I have several of these I could post photos of). When I spoke to the representative from Pannier, he told me the way the older signs were produced was by essentially laying a paper sticker onto compressed cardboard then rolling fiberglass over top to get the finished product. But if this person was answering my questions, he likely isn't out on the floor making them so this could be inaccurate. Regardless, I find it amazing that this company still has the blueprints to make these, and could do so for collectors, but SEPTA wants no part of it, essentially leaving another small bit of our transit history to rot, albeit much less significantly than real infrastructure.
To nomis and Mr. Mitchell - thanks for your help with what the coding could be. They sound like good answers.