Usually the annunciators were installed and connected directly to the dispatchers telephone pair which was two of the wires on the crossarm.
It is unlikely that the "extra" wires on the side brackets on the poles west of Antonito were used for an annunciator circuit, because the dispatchers telephone pair
was already available on the line going past MP 289 to connect it to.
I still think the extra wires on those brackets was for a telephone line (maybe from Mtn Bell) out to the old section house that was located in the valley away from the right of way where the tracks looped around starting on the climb east of Big Horn..
Probably no way to verify it at this late date, it's been gone for over 50 years.
ET