I published an open paper that describes a little crazy (but seems to be novel) idea of combining digital sound and QR codes together. The paper briefly describes a new approach that brings quite effective and easy data hiding and watermarking technique to general public through the use of QR codes (or similar bar-codes).
Read the paper: Alex Radzishevsky, Visual Domain Audio Watermarking (VDAW) and Spectral Barcode Audio Watermarking (SBAW), February 2014.