The renderings in the Chrysler Canada brochure from 64 show an inset Pontiac triangle in the center of the grill. The other 9-code Signet's that I have seen also have that style of grill (not the one that is on this car). Not sure where this one came from.
Perhaps there's someone who can ID?
I could see on the back side where perhaps there was a surface-mounted badge at some point, but the car had all badges and trim removed some time back.
