Apparently the 6 had a 3M material in the number 5 over it which reflected 5 toward theadlights.
In daylight we saw 65. At night 5 was reflected toward the driver so we saw 55.
When? Where? Still in use?
The railroad grade crossing signal [STOP ON RED SIGNAL] black sign had glass marbles (“cat eyes”?) in the white letters to reflect light back toward the source.
As a child I recall the glass marbles did not reflect very well.