What are those mysterious marks?
They are QR codes.*
A QR Code is a matrix code (or two-dimensional bar code) created by Japanese corporation Denso-Wave in 1994. The "QR" is derived from "Quick Response", as the creator intended the code to allow its contents to be decoded at high speed.
QR Codes are common in Japan, where they are currently the most popular type of two dimensional codes. Moreover, most current Japanese mobile phones can read this code with their camera. They are here too and you will see more and more of them.
Some phones come with QR code software. For iPhones, download the free “QR App” or the “QuickMark QR Code Reader”, or others. Or go to Kaywa.com and create your own.
Note: In many cases, all you have to do with your iPhone or iPad is use the Camera app and simply point it to any QR code (like the ones on this page) - no pressing shutter button necessary! It will offer you a website to visit. Wikipedia link: https://en.wikipedia.org/wiki/QR_code
* Scan the QR codes on this page with your phone and they will reveal messages or take you to special places on the web! Make sure you scan only one QR code at a time.You can block part of the other codes that you do not want to scan by putting your finger in front of them so you only scan the one you want. (Yes, each one is different.)