24. March 2016
As described in Part 3 of ISO 7816 specifications, the ATR is a sequence of bytes sent by the microchip when replying to a RESET signal. In practical terms, each RESET operation induces on the I/O contact a microchip’s reply constituted by up to 33 characters coding a set of information relating to microchip’s characteristics such as: supported transmission protocols, installed operating system, microchip’s version and manufacturer and so on.
The manufacturer part of the ATR and the ones related to operating systems and microchip's version uniquely identify a smart card.
I found and interesting page that reports the most of the smart card on the market with its own ATR: