QR Codes could be most effective way of offilne marketing nowadays. At least, I would print flyers and posters for any of my Mobile App or Website to market it. When you technically implement code right, then anyone passing the poster or seeing flyer could take the mobile device and will be directed to your offering.
I'm not sure how effective is to put QR codes to your Youtube videos, website, etc as basic link does same job with less of hassless.

Veiko Herne