three generations of MaBell's 'buried cable' markers

This trio are some of my smallest signs, measuring only 3-1/2" x 7". Little signs similar to this are (were?) fastened near the base of utility poles to show where underground telephone cables were also present. Nowadays I doubt they bother with such niceties in the ever changing world of telephony, being more likely to stick up a series of shorter posts with slightly larger metal signs on them or even shorter little plastic marker thingies. (I have a couple of those metal signs too already shown here somewhere) They have been collected over the years, and represent 3 different eras I guess.

The dark blue and white is no doubt the oldest, being made of heavy enameled steel with brass ferrules. The orange one would be in the middle of these three somewhere, note the phone number it directs one to call. (it is also the only one with such further info on it) The light blue would be newest, and is also NOS (new old stock) not having seen time on a pole as the other two have. The newer two are aluminum instead of steel, never having had ferrules.