Who is "A.F."?

Ted Wilush replied:

Hey Paul,

Your insulator is a Canadian Porcelain M-3733 and was used en-mass on the old T-N line as replacements for the original M-3740s, installation would be mid 1920's. The A.F. marking is a mystery and is also found on a number of other CP multipart styles manufactured around the same time. Interestingly CP very rarely marked their larger insulators with their name during this period.

Thanks Ted!