One dot above T, R, E, or X gives the quarter of the year the glass was manufactured: T = Jan, Feb, March, R = April, May, June, E = July Aug, Sept, X = Oct, Nov, Dec. Nine letters make the word TOUGHENED, one dot below a letter gives the year of the decade: T = 1 O = 2 U = 3 and so on. Say your car is a 1950's MG, then TRIPLEX TOUGHENED, with one dot over the 'R' in Triplex, and the other under the last 'E' in Toughened, indicates 'April/May/June 1958' Below are some date code pictures.
Don’t worry about the return long distance, my phone service is worldwide.
You are welcome to come by for a personal visit, but for your convenience you really should call first to make sure that I will be in the shop.
Triplex windows manufactured in the 1950s through the late 1970s can be dated with the "Triplex code" etched into the glass.
Assuming that your car has the original glass, it can be used to fairly accurately date your car.
My 75 GT has Sicursive side glass but a Triplex heated back-light with a code that fits the date of build of the car.