I can’t recall where I read this, but it is a good ”thing to know” if you’re looking to replace the rear lens of your Federal siren: Apperently, Federal used the tail light lens from the 1954 Oldsmobile! Very easy to source on FleaBay.
@Skulldigger, I was thinking of you when I posted this...I couldn’t remember if was a Federal siren or something else. I recall you thread on making your own replacement. Here’s a site that may help you in your next attempt:
How you can replicate a tail light lens of any car using optically-clear resin.
Good to know @cmb56. That pretty much tells me it was originally an Olds
lens used by Federal. Guide is almost exclusively GM and they always incorporate the model year in the last two digits in the part number (that’s how you can identify the year of a classic auto, in case you were wondering if you were looking at a 62 or 63 Impala).