In computer networking, Semaphore Flag Signaling System (SFSS) is a humorous proposal to carry Internet Protocol (IP) traffic by semaphores. Semaphore Flag Signaling System was initially described in RFC 4824, an April Fools RFC issued by the Internet Engineering Task Force edited by J. Hofmueller, et al. and released on April Fool's Day 2007. It is one of several April 1 RFCs.
A reference implementation of IP over SFS has been done by the authors of the RFC within the project "Talking the Fish". An email was transmitted using SMTP over Semaphore Flag Signals.