UTM Link Builder + QR Code
A printed QR code looks the same whichever poster it is on. Add UTM tags to the link and Google Analytics (and most other tools) will show how many visits came from which flyer, poster or message. This tool adds the tags, keeps the rest of your address, and gives you the QR code and the tagged link.
The three required tags are source (where), medium (what kind) and campaign (which promotion). Keep names consistent: Flyer and flyer count as two different sources, so the lowercase option is on by default.
For many links at once use the link QR code page; to make the code look good use the styling tool.