Is this what you are talking about? The pic below shows the device that is on my 1928 Canopy Express.
I cannot verify that it is in the original position, but I suspect it is.
The spring is broken. I suspect it would normally be in an upward position. You can see the dent in the top window sill where the anti-rattle roller hit the top, thus, keeping the window from rattling.
The body on my Canopy Express was made by the Hercules Body Company, so this little device was part of the hardware that they used.
Cheers, Dean