It's tongue-in-cheek, implying that many people working with the stuff already lost an eye to it.

It's part joke and part telling people "hey, this stuff is really dangerous, take it seriously or you'll lose an eye, or both". I don't think I've seen a single lab with high-powered lasers that didn't have a variant of this sign.

A similar popular sign for chemical labs is "Carol Never Wore Her Safety Goggles. Now She Doesn't Need Them", depicting a blind woman with sunglasses and a white cane. (https://knowyourmeme.com/memes/carols-safety-goggles)