Semaphore telegraphs are also called, "Chappe telegraphs" or "Napoleonic semaphore". Such critical sections are protected using a synchronization object such as a semaphore or mutex. Alternatively a mutex could be used in place of the binary semaphore. Operation V increments the semaphore "S", and operation P decrements it. The simplest type of lock is a binary semaphore. Signalling by means of indicator pointers was called "semaphore". The railway is controlled by lower quadrant semaphore signals. SystemVerilog offers two primitives specifically for interthread synchronization&colon; "mailbox" and "semaphore". The traditional semaphore turn signals were replaced by conventional flashing directional indicators worldwide. Barriers are typically implemented using a lock or a semaphore. Signals can be sent by flaghoist, signal lamp ("blinker"), flag semaphore, radiotelegraphy, and radiotelephony. The current system replaced 1950s-era semaphore signals. The letters of the flag semaphore are also a common artistic motif. This is to be distinguished from "semaphore", which merely transmits messages. The function tries to grab the console semaphore (console sem).