Flanger signs on the NYC

Doing research for a model railroad project. Help me understand how flanger signs were used, where they were installed, and what different versions of blades meant. I've seen them trackside for years in NYC Lines East territory, but never gave them a second thought.

I have seen a flanger sign with one blade as the most common, but there are others I've seen with two blades.

How were they painted? Where were they installed? What did the different blades mean?

Any help would be appreciated.

-otto-

.....and then I just found this.
Here's where I found it.

http://www.multimodalways.org/archives/ ... Plans.html" onclick="window.open(this.href);return false;