I know this is almost a decade old and I apologize for dredging this up, but I have relevant information to contribute. I personally believe the switch to Federal Sign and Signal from Enterprises occurred at some point in 1955, as last year I was looking at the USPTO website and found a document dated 31 May 1955 ( for something relating to the Thunderbolt trademark) in which Federal Enterprises was listed as at the time presently trading as Federal Sign and Signal. This document is USPTO Case #71628684, page 19. I will link it below. I'm also investigating when the Electric to Enterprises switch occurred. I personally believe it occurred after WWII, possibly around 1950. Why I believe this is the case is the fact that the earliest mention of Federal Enterprises I have been presently was from a January 1950 dated trade catalog that I would have to go hunt for again, however I have not found any legal documentation pertaining to the name change as of yet. To go to one last topic that is also relevant, the name switch from Sign and Signal to Signal was executed on February 4, 1976 (and if I am not mistaken, was applied for August 29, 1975 per the conveyance) which can be found on page one on the document linked below:
https://tsdr.uspto.gov/documentviewer?c ... =18&page=1