Did you know that on progressive lenses, it is?
Yes, right there on the lens. It's hard to see of course, you may even have trouble finding it on your own pair (and you'll definitely need another pair of glasses to see it!). The trick is to be at the right angle (straight on), and to focus right on the lens and not through it. I have been unsuccessful in photographing this, so I have done a Paint Shop tweaked image to assist you.
About halfway up each lens, towards the outer edge, is a deeply embedded "watermark". You'll see a tiny circle, diamond, oval or similar symbol, and directly under it is the strength of the add. A +1.00 add is shown as 10, a +1.50 add as 15, and a +2.00 add as 20, and so on. Sometimes there is a 0 before this, i.e. 015. It's not an EASY thing to spot, but it's there. So practice a bit, and soon you'll have another way to drive yourself crazy!