Mark metal-tile-glass with your laser using CerMark! CerMark is proven durable with over 15 years of durability testing including by NASA. Only CerMark produces the darkest and most consistent marks on a variety of materials. http://www.LaserBits.com
I just received the shrink wrap sleeves yesterday, but haven't had a chance to use them. They appear to be the perfect size for mugs, so looking forward to using them on a project.