1) Declare a marketing custom source for QR Codes and apply a campaign to each QR Code for instance.
Tools > Sources and campaigns > Marketing campaigns > Custom > Sources: add a new Source for which you can add as many variables as needed. Please note that only variable C is required to declare the source. Here the source can be named QR Codes.
2) Tag the link in the QR Code.
The direct method should be like: https://www.site.com#xtor=CS1-2