Smiling is universal – it means the same thing in every language across the globe and is even seen in some animals. From the people you pass on the street to your best customers, everyone knows that you're in a good mood just with a simple smile.
Starting in elementary school, teachers give smiley stickers to reward good behavior or to note an assignment well done. As we get older, stickers aren't given as readily, but teenagers and adults alike have begun using simple emojis to express themselves. And while emojis have become more and more complex (smiles, frowns, flowers and hearts), it all started with a simple colon and half a parenthesis. :)
For businesses, it's easy to use this universal symbol to show appreciation to your customers. Use them to showcase a product that's on special, so it stands out from your other products. Stick them to the side of a bag before you hand merchandise over to a customer. Or add a smiley sticker to the bottom of an invoice. Don't think a simple smiley face sticker is worth the effort? A study conducted at Cornell University showed that waitresses who wrote smiley faces on the bill got bigger tips. [source: https://money.cnn.com/2004/08/24/commentary/everyday/sahadi/]
A little appreciation goes a long way. And something as simple as a smile is an easy way to show it.