Question:  How does an IISNS mounting work? 

Answer:  Internally Illuminated Street Name Signs are typically mounted under a traffic signal mast arm.  Older style signs are typically light be fluorescent tubes and new style signs are LED.  The mountings connect the sign housing to the mast arm, and are hinged so the sign can swing in the wind and reduce what would otherwise be a large wind load.  The photo shows a close up of an IISNS from Alameda County.

There is a base that connects to grooves in the sign frame with four small bolts.  There is a hinged connection with a bolt that connects to another vertical bracket that goes toward the mast arm.  There is one bracket assembly on each end of the IISNS, and the vertical bracket can be cut in any length so the sign will hang level.