Dear Patrick,
> I've been trying to research the date a particular sign was posted on
> my property in Glendale, California. When I saw that it had the
> company's name (Pacific Fence Co.) and a very old 2L-4N phone
> number ( Hillside 8141 ), I grew to wonder when Los Angeles would have
> made the transition to 2L-5N, because I could probably figure the sign
> predates that time.
Unfortunately, the 2l-5n transition date won't be much help in dating the sign's installation.
Signs of the type you describe are often made in high volume and will be used until the stock is exhausted even if the number if partially obsolete. I've seen a great many such signs still in use where the phone number was partially obsolete. For example, signs for a cab company in a small town still had the old 5 digit number rather than the current 7 digit number. So, the sign/fence could've been installed well after the conversion.
Another possibility is that the fence was second-hand and in use before used on your property.
Postal zip codes came out around 1964, but it took years for people to change their addressing from the old zone system ("Philadephia 50, PA") to zip code ("Philladelphia, PA 19150".
There is a highway company whose trucks to this day still say "DE 3" on them. (I wanted to take a picture the other day when passing a work area, but there was no place to safely pull over, plus taking pictures these days of public works evokes suspicion and maybe a police inquiry.)
One of the reasons we have mandatory ten digit and area code overlays is to avoid splits for forcing people to get a new area code. That's a nusiance for business people who must print up new stationery, change their advertising, alert customers, etc. I'm lucky in that I still have my original area code. My region had one split and I stayed on the old side of the boundary. Even my cell phone is the old area code. But now we have overlays. I'm glad I don't have a new area code, I can't even keep track of them.