QR codes are great for products and menu items if users need more info. As to being used on signs... i dunno about that. you have to take out your phone, launch an app (assuming you have an app that reads qr code), point and click (w/enough lighting and focus/distance) just to get to your data.
that said, you can use that coupled with a ph# AND website that's easy to remember... most importantly is tracking your leads. w/today's tech, you can easily qualify/quantify the effectiveness of your medium by use of link tracking / web analytics and ph# tracking ... that's the only way you'll truly know which medium is working best for you or at least how effective they are for people getting back to you.
btw, i say menu items (i.e., restaurants - if ppl want to know nutritional data, origin, price, reviews, etc.) or products (i.e., similar to restaurants if you're at a grocery/food place OR for mfr data, reviews, coupons, rebates, price check, etc.)... note that above mentioned uses are typically where you're not in a car or getting a single letter/post card that you're reading (and you have to pull out your phone just to scan the qr code vs. typing in a url or ph# just to call/get more info). if i were to guess, qr code is best used for more data on items OR as a shortcut to some long url link that would save the user time than typing it in.
