Good observation, jdowling. I have no idea what it was used for, but a digital number display is exactly what it is. The seemingly random arrangement of the "pixels" is so that the digits are nicely formed. I can just barely remember the change (in the Fifties) of the scoreboard at the high-school football stadium from one like that to the newer "7-segment" concept.

The originals, like the one here, were an electric nightmare (calling them "electronic" was decades in the future) requiring incredible amounts of wiring, switches, and relays, and broke down very often. Perhaps that's why this one isn't lit.

[We've since learned it's a carriage call. - tterrace]

Under the Nixon sign and at the street curb, on the pole. It appears to be a three character dot matrix display.

This is the second such display I've seen in a Shorpy photo. I've Googled several phrases but can't find anything like it. Anybody?

The Nixon stood till 1950 when it was torn down to make room for the (ugly) former Alcoa HQ.

http://www.post-gazette.com/pg/10122/1054577-426.stm

The Nixon-Nirdlinger family owned and ran the Nixon Theatre. Sam Nixon passed away in 1918, and the business passed to his son Fred. Fred had a remarkable ability to keep wedding cake companies in business - marrying five different women, the fifth one twice. Fifth wife Charlotte Nixon-Nirdlinger shot and killed Fred on the French Riviera in 1931, and was eventually acquitted on the grounds of self-defense. In 1931, Sam's grandson Sam took over the theatre. It was demolished in 1950, for a new Alcoa building.

Below is the same view from July of 2016.