Z87.1
Remember folks, if you are ever going to use these as shooting glasses, you really do want ones that are safety rated. Z87.1 is not only for strength, it means they meet optical clarity standards, as well.
Oakley and Gargoyle meet or exceed Z87.1 testing. That is a lot of what you are paying for when you buy them.
Smith does not. I contacted them to verify it. They refuse to accept the liability implied by saying they meet that standard. They meet the slightly lower Z80 standard.
If you buy $15.00 sunglasses off a table at a show, you have no way of knowing whether they meet the standard, even if they have a label saying they do. Sorry, but that is the way "knock-offs" work.