The W is implies as winter. Basically on the coldest day of the year in winter 5w-30 will have the viscosity of 5 weight oil of that particualr temp. (no temp is specified) and a the second 2 digit number is the viscosity at 100 degrees centigrade
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I mean M
The South Will Rise Again
castrol 10 w 40 high mileage
They stand for the letters E and W.
This is a guess: the dot distinguishes i from the peaks in the cursive letters u and w.