Byline: Mark Bridge Technology Correspondent
Emojis may seem like a bit of fun and nothing more but it turns out they are another tool to help businesses sell you stuff.
Twitter now enables advertisers to target the people who tweet more than 3.2 billion smileys, thumbs-up and their like each year.
Although agencies say this means that people see more relevant adverts, the practice has been criticised by campaigners.
Ad-targeting based on emojis works on the straightforward principle that someone who posts a lot of pizza emojis, well, probably likes pizza and a frequent user of beer emojis almost certainly enjoys a pint.
More significantly, the emojis can help industry algorithms to predict whether the sentiment behind a tweet is positive or negative. This can be very difficult for artificial intelligence to determine based only on a sentence or two of text.
Someone who posts about a luxury brand and includes a "smiling face with heart-eyes" is probably more susceptible to its ads than someone using the "swearing face", the thinking goes.
There are early indicators that the tactic may work. According to 4C Insights, an ad agency, one commercial for a fast-food company received almost three times as many likes, retweets and comments when it targeted people based on emojis as when it used more traditional criteria.
Analysts believe the practice could spread to other social media as the use of emojis becomes more entrenched.
While some are easy to interpret, others such as the "upside-down face" are ambiguous. In these cases, algorithms can use the context of a tweet to guess whether it is being used in a positive or negative light.
Earlier this year, Toyota released 83 versions of one Twitter ad and targeted users based on their emoji posting. The premise of the ad was simple. People who had recently posted using a particular face emoji, such as a smiling or frowning face, saw a character with that face driving a Toyota Camry car.
Jamie Court, president of Consumer Watchdog, a US group, told the Marketplace website: "That's really inappropriate. When companies start to create a psychological profile of people based on their emotions and then advertise to them based on that profile, that's intrusive."
Citing a hypothetical example, he added: "People are not used to tweeting an emoji for a piece of pizza then getting an ad for Weight Watchers."
The industry defends its analysis of emojis as consistent with its trawling of our written words and other data. Aaron Goldman, of 4C Insights, told the Vox website: "You shared that data freely, with a free website that is adsupported. You should be able to understand that [this] type of thing is going to happen."
The targeting of ads based on emotions is controversial. Last year Facebook was criticised after leaked documents indicated that the social network told advertisers that it could identify when teenage users felt "insecure" and "need a confidence boost". It claimed the algorithm could detect from their posts if users felt "overwhelmed", "anxious" and "a failure". Facebook claimed that the reports were "misleading" and it did not "offer tools to target people based on their emotional state".