If you’ve ever ended an e-mail message or an instant message with an emoticon, now might be a good time to pause and reflect on the work of Scott E. Fahlman. After all, it will be 25 years ago tomorrow that Mr. Fahlman, a professor of computer science at Carnegie Mellon University, invented the digital smiley face.

After a colleague joked about a contaminated elevator on an electronic bulletin board, Mr. Fahlman had his eureka moment: He recommended that future quipsters mark their jokes with “:-)” to make sure no one misconstrued their comments.