There are a number of identifying white markings on a horse's face and they are so common they have their own names.
A Guide to Horse Markings
Intro to Face Markings
Horse Face and Leg Markings - Horse Illustrated
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Horse Markings 101
Your 4-H Horse: Care, Management, and Horsemanship
The Mane Point: Stars and Stripes, Snips and Stripes