Oddbean new post about login | logout @93672b44 Take heart, the markings are typically on the outside and you can easily get ones with markings cast with the glass (though they are more difficult to read).
@981de366 If you're washing them in the same water as other dishes (like a dishwasher), lead and the like is going to leach onto other surfaces. I'll be replacing mine with ones that have the markings cast into the glass.