The white liquid is heated thermoplastic road marking, used here like a paint. After it's applied, a second layer of reflective glass beads is spread over it, so that the glass beads embed in the thermoplastic before it hardens.
https://diqn32j8nouaz.cloudfront.net...ad_marking.gif
The video shows similar triangle markings. They're pre-made to shape in advance, then placed on the ground, heated, and covered with reflective glass beads.
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