The original source (thanks to my contact Ballester-Olmos) is the APRO Bulletin, March-April 1967, p 1.
The original photograph was published by APRO, which withheld the photographer´s name on request, and strangely it received no analysis in the
following years. US engineer Larry Robinson believes it is simply a suction cup stuck to a car window, but it was just an opinion. (thanks to
Ballester-Olmos for the informations)
A preliminary work on the best photo resolution reveals some interesting things nonetheless:
So, not a smoking gun yet, but IMO a strong clue to what it could be, i-e some sort of pendulum suspended by one or two strings (Though I wasn't able
to see two after the enhancement...)
edit on 10-1-2013 by elevenaugust because: (no reason given)