Texas Ranger,
it was written that his were wired in series, from my experiences the exit signs were fed with 120v and in Chicago, were ALL fed from a fused panel. but the lampholders were not series'd if that were the case ordinary lamps would have worked just fine for longevity
it was their Code through the late 70s and may still be a requirement
my apologies for adding my own brand of confusing Hoosier gibberish....
