To mark the anniversary Wednesday, Fahlman and his colleagues are starting an annual student contest for innovation in technology-assisted, person-to-person communication. The Smiley Award, sponsored by Yahoo Inc., carries a $500 cash prize.
Language experts say the smiley face and other emotional icons, known as emoticons, have given people a concise way in e-mail and other electronic messages of expressing sentiments that otherwise would be difficult to detect.
Fahlman posted the emoticon in a message to an online electronic bulletin board at 11:44 a.m. on Sept. 19, 1982, during a discussion about the limits of online humor and how to denote comments meant to be taken lightly.
"I propose the following character sequence for joke markers: :-)," wrote Fahlman. "Read it sideways."
The suggestion gave computer users a way to convey humor or positive feelings with a smile - or the opposite sentiments by reversing the parenthesis to form a frown.
Carnegie Mellon said Fahlman's smileys spread from its campus to other universities, then businesses and eventually around the world as the Internet gained popularity.
Computer science and linguistics professors contacted by The Associated Press said they were unaware of who first used the symbol.
"I've never seen any hard evidence that the :-) sequence was in use before my original post, and I've never run into anyone who actually claims to have invented it before I did," Fahlman wrote on the university's Web page dedicated to the smiley face. "But it's always possible that someone else had the same idea - it's a simple and obvious idea, after all."
Among the first variations were Smiley with glasses 8-) and the winky ;-). Some hobbyists have gone so far as to create celebrity emoticons ranging from Homer Simpson to Harry Potter, according to a press release from Carnegie Mellon.
Today people can hardly imagine using computer chat programs that don't translate keystrokes into colorful graphics, said Ryan Stansifer, a computer science professor at the Florida Institute of Technology.
"Now we have so much power, we don't settle for a colon-dash-paren," he said. "You want the smiley face, so all these chatting softwares have to have them."
Instant messaging programs often contain an array of faces intended to express emotions ranging from surprise to affection to embarrassment.
"It has been fascinating to watch this phenomenon grow from a little message I tossed off in 10 minutes to something that has spread all around the world," Fahlman was quoted as saying in a university statement. "I sometimes wonder how many millions of people have typed these characters, and how many have turned their heads to one side to view a smiley, in the 25 years since this all started."
Amy Weinberg, a University of Maryland linguist and computer scientist, said emoticons such as the smiley were "definitely creeping into the way, both in business and academia, people communicate."
"In terms of things that language processing does, you have to take them into account," she said. "If you're doing almost anything ... and you have a sentence that says 'I love my boss' and then there's a smiley face, you better not take that seriously."
Emoticons reflect the likely original purpose of language - to enable people to express emotion, said Clifford Nass, a professor of communications at Stanford University. The emotion behind a written sentence may be hard to discern because emotion is often conveyed through tone of voice, he said.
"What emoticons do is essentially provide a mechanism to transmit emotion when you don't have the voice," Nass said.
In some ways, he added, they also give people "the ability not to think as hard about the words they're using."
Stansifer said the emoticon was part of a natural progression in communication.
"I don't think the smiley face was the beginning and the end," he said. "All people at all times take advantage of whatever means of communication they have."