The check-in QR codes work with the new NHS app to help fight the spread of coronavirus. Register online to receive your official QR code digitally which you print off so that your clients can check in when they arrive.
The venues which are required by law to display these are listed on the government website. Generally these are places where the dwell time for clients is significant, which wouldn’t apply to take-aways or shops. There is more information from Kent Trading Standards.