Revolutionizing the cash register receipt sounds like the worst kind of startup cliché, but indulge me for a moment.

Today, Square is unveiling a new feature for its digital receipts that, in and of itself, doesn't radically change how we interact with the places where we shop. But it points us in this direction. And it starts with a smiley face.

Square is best known for its new-age credit-card readers, which plug into the headphone jack on a smartphone or tablet. It's pretty cool, but for the merchants of the world, the meat and potatoes is Square's Register app. One of Register's basic features is the ability to send electronic receipts. The first time you swipe a card on Register, you're asked for an email address or SMS contact number so the merchant can send a receipt. Provide one, and every time you use that card, your contact info is right there, no matter where you are. In that way, your credit card is like your avatar. It's your identity on Square.

>Square is unveiling a new feature for its digital receipts that, in and of itself, doesn't radically change how we interact with the places where we shop. But it points us in this direction.

Now, along with all the standard information about your purchase, merchants also have something else they can slip right in the receipt: a request for feedback. Tap on a smiley face or a frowny face–yes, really–and you're taken to a screen with a series of checkboxes where you rate various aspects of the purchase: wait time, customer service, quality, and "other." Finally, and most importantly, there's a text box for leaving a detailed complaint or compliment. Of course, product and store reviews are as old as Amazon and Yelp. But what Square is offering is different in important ways. Unlike those other sites, this receipt-based feedback is a direct, private line between you and the merchant.

To be sure, there's always the option of–shudder to think–a face-to-face conversation. And on the level of "my coffee is cold," you don't really need an app for that. But what building feedback into a digital receipt does so well is set the stage for a genuine ongoing conversation. On the backend, the exchange between stores and their customers looks like nothing so much as a messaging app, with little back-and-forth conversation bubbles, much like iOS Messages or WhatsApp. Again, the concept of messaging may seem so obvious that it's not worth noting. But since when did a business give you an instant, personal way to ping it across the checkout counter? How might the way you imagine your relationship with that restaurant or grocery store or hardware store change if you started to relate to it less like a business and more like a group of real people?

As we know all too well, the prospect of public shame is not enough to quell the petty vindictiveness and first-world consumer hyper-entitlement on Yelp. But–and I can't believe I'm saying this–that doesn't mean all Yelp users are as awful as they seem. Yelp's quasi-anonymity extends not just to reviewers, but to the businesses being reviewed. Yes, those businesses can opt to respond on Yelp to customer complaints. But it's all too easy to be nasty when the business being pilloried doesn't have a face. And, on top of that, a Yelp page is better suited to venting than problem solving because it's indirect. Maybe if you shout loud enough, the business will fix the problem. But that's not the explicit priority built into Yelp's design.

The chance to get a complaint addressed on the level of a receipt, on the other hand, couldn't be more direct. And with that option available, the onus is put on customers to decide if they really want to have their problem fixed, their frustration addressed by going directly to a business, or if they're really just interested in being spiteful by posting a negative review online.

As for compliments, a business might prefer that customers go on Yelp and publicly shower it with praise. But direct, private praise creates a positive feedback loop that helps businesses understand what they're doing right and cements customer loyalty by fostering a feeling of connection.

In either case, what really has the potential to happen is the same kind of intimate back-and-forth that makes messaging in general so compelling. And Square is smart to see that the receipt can start to be the medium by which those messages are exchanged. It's not seamless: for customers, the full feedback process ends up taking place through the smartphone browser. It's not pure messaging, at least not yet. But it starts to take on those contours.

>For businesses, paper receipts are a wasted opportunity. Here is a piece of printed matter every business gives every customer every time something is bought.

For businesses, paper receipts are a wasted opportunity. Here is a piece of printed matter every business gives every customer every time something is bought. Yet they may be the most-used, least-read medium of information transfer ever, widely seen by most of us as pointless clutter.

By making receipts digital, they become not all that different from any other kind of messaging we all do on our mobile devices. Even without a feedback option, digital receipts are easily stored, searched, and collated. By adding a messaging capability, Square is setting up the possibility of a new kind of expectation, one that could become a default assumption around how customers interact with businesses.

If a paper receipt is trash, a digital receipt is by definition a platform. As trite as that may sound, it's a way to communicate between consumers and businesses that's ripe for new tools to be built on top of it. And as many of us know, once messages start flying back and forth, they can be hard to stop. Especially for the generations that grow up knowing nothing but smartphones, the idea that you couldn't message with that person at the counter might seem pointlessly irritating. Of course, that should be an option. With feedback, Square is turning receipts into another way to talk.