12-12-8 Signals

[Amtrakprod]

I've found these signals interesting, let's look for them on G maps: https://www.google.com/maps/@42.2602559,-71.4648009,3a,30.7y,146.93h,95.12t/data=!3m6!1e1!3m4!1sWY_oBcglnXpkOV4uBGto4w!2e0!7i13312!8i6656
https://www.google.com/maps/@42.3983396,-71.1745866,3a,21.5y,23.94h,95.01t/data=!3m6!1e1!3m4!1sVZlOy8qJ0Z1PFl1sfDw50w!2e0!7i13312!8i6656
https://www.google.com/maps/@42.4009803,-71.1165571,3a,75y,41.2h,83.8t/data=!3m6!1e1!3m4!1szHDfy8C1XiKkFQW9BhdOMg!2e0!7i13312!8i6656
https://www.google.com/maps/@40.8829652,-74.557288,3a,27.2y,358.25h,91.23t/data=!3m6!1e1!3m4!1swER0RC9-pfRCcbuVnynZDQ!2e0!7i13312!8i6656
Now you guys find some!!!!

[Big John]

12-12-8 should be used in emergency signals: https://mutcd.fhwa.dot.gov/htm/2009/part4/part4g.htm

[roadman65]

In Florida they are used on Emergency Signals.  The yellow flasher is usually 8, but the middle yellow for when the light is about to turn red and the actual red are both 12 inch lenses.

[Amtrakprod]

They are very commonly used on Railroad Crossing Traffic lights too


iPhone

[PHLBOS]

I've found these signals interesting, let's look for them on G maps: https://www.google.com/maps/@42.2602559,-71.4648009,3a,30.7y,146.93h,95.12t/data=!3m6!1e1!3m4!1sWY_oBcglnXpkOV4uBGto4w!2e0!7i13312!8i6656
https://www.google.com/maps/@42.3983396,-71.1745866,3a,21.5y,23.94h,95.01t/data=!3m6!1e1!3m4!1sVZlOy8qJ0Z1PFl1sfDw50w!2e0!7i13312!8i6656
https://www.google.com/maps/@42.4009803,-71.1165571,3a,75y,41.2h,83.8t/data=!3m6!1e1!3m4!1szHDfy8C1XiKkFQW9BhdOMg!2e0!7i13312!8i6656

Given that your first three examples are all in Massachusetts.  Here's three more from the North Shore (Peabody):

MA 114 (Gardiner St.) at Abington Ave./Seneca Rd.

Central St., one surviving original signalhead (when new, this pedestrian crossing-only signal all featured 12-12-8 heads)

Central St. at Warren St. (the signalheads on the left (east side of Central) are the original signalheads). 
Note: the Warren St. signalheads feature all red lenses (the middle lenses were originally yellow).