@ACG2 It's to keep drivers alert.
Human brains look for faces. It's why you faces in buildings and scribbles on the sidewalk. Having eyes on the truck makes drivers see it, and it wakes up the brain and makes you more alert. It's significantly reduced truck-involved traffic accidents (specifically rear ending trucks).
@ACG2 They tested it here in 2020 or 2021 and now it's very common to see eyes on the backs of trucks. The ones I took a picture of are probably the most common, but they come in all colors and shapes with a wide variety of styles. It's fun.
@LianaBrooks that’s a terrific idea ( as one who lives with Lots of truck traffic ) for busy corridors.