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Signal for Help

Signal for Help: a silent one-handed gesture (open palm, tucked thumb, fingers folded over) created by the Canadian Women's Foundation in April 2020 during COVID-19 lockdowns, letting people in danger discreetly ask someone to check in safely; viral on TikTok, used in several rescues, with known recognition limits.

Signal Foundation

The Signal Foundation, formally the Signal Technology Foundation, is an American nonprofit founded in 2018 by Brian Acton and Moxie Marlinspike to support the Signal messaging app.

Signal generator

A signal generator, also known as a frequency generator or test oscillator, is electronic test equipment producing signals with controllable frequency, amplitude, and modulation for testing devices.

Signal modulation

Signal modulation is the variation of a carrier wave's amplitude, frequency, or phase so that it carries information, underlying AM and FM radio, broadcasting, and digital schemes like QAM.

Signal Peak (coal mine)

Signal Peak, formally Bull Mountains Mine No. 1, is Montana's only underground coal mine, located in the Bull Mountains near Roundup and exporting most of its coal to Asia.

Signal peptidase complex subunit 3

SPCS3 (SPC22/23, SPC3) is an essential non-catalytic subunit of the ER signal peptidase complex, a 180-aa glycoprotein at human 4q34.2 required for signal peptide cleavage and linked to HIV-1 and chikungunya virus restriction.

Signal peptidase complex-like protein DTM1

Signal peptidase complex-like protein DTM1 (DEFECTIVE TAPETUM AND MEIOCYTES 1, LOC_Os07g43010) is a 112-aa rice ER membrane protein of the SPCS1 family, present only in cereals, required for early tapetum development and meiosis; disruption causes male sterility.

Signal peptide

Signal peptide: N-terminal peptide directing protein secretion via SRP, Sec, or Tat pathways; tripartite N-H-C structure, 15-30 residues, cleaved by signal peptidase; Tat type carries twin-arginine motif.

Signal phase and timing (SPaT)

Signal phase and timing (SPaT) is a message type in the SAE J2735 V2X standard that broadcasts a traffic signal's current and upcoming states to connected vehicles.

Signal processing

Signal processing, also called signal theory, is a branch of electrical engineering and applied mathematics that analyzes, modifies, and synthesizes signals like sound, images, and radar returns.

Signal Protocol

The Signal Protocol, formerly known as the Axolotl protocol, is an open-source cryptographic specification providing end-to-end encryption, used by the Signal app, WhatsApp, and Google Messages.

Sep 29, 2026

Signal separation

Signal separation, also called blind source separation (BSS), is a family of signal processing methods that recover individual source signals from observed mixtures without knowing the mixing process.

Signal station

A signal station is a tower or building used to send messages to vessels or other stations using signals such as flags, fires, and lights.

Signal temporal logic

Signal temporal logic (STL) is a temporal logic for specifying and monitoring properties of real-valued, dense-time signals in cyber-physical systems, analog circuits, and systems biology.

Sep 29, 2026

Signal timing

Signal timing is the traffic engineering method of setting green, yellow, red, and all-red intervals, cycle length, green splits, and offsets between adjacent intersections to control vehicle and pedestrian flow.

Signal transduction

Signal transduction, also known as cell signaling, is the process by which a cell converts signals such as hormones and growth factors into specific responses via receptors and second messengers.

Signal transduction histidine kinase, hybrid-type, aerobic respiration control ArcB

ArcB (aerobic respiration control sensor protein, UniProt P58363) is the hybrid histidine kinase of the E. coli Arc two-component system. It signals to ArcA solely via a His292-Asp576-His717 phosphorelay and senses redox through the ubiquinone:ubiquinol ratio.

Signal transduction histidine kinase, osmosensitive K+ channel sensor, N-terminal

KdpD N-terminal domain (InterPro IPR003852), cytoplasmic ~210 aa sensor domain of osmosensitive K+ channel histidine kinases; Walker A/B ATP-binding, Usp domain; atypical serine kinase inhibiting KdpFABC; prototype E. coli KdpD/KdpE system.

Signal transduction response regulator, phosphate regulon transcriptional regulatory protein PhoB

PhoB is the cytoplasmic response regulator of the PhoR/PhoB two-component system in Escherichia coli; phosphorylation by PhoR under phosphate starvation activates dimerization, Pho box DNA binding, and transcription of the phosphate regulon.

Signal Transfer Point

A signal transfer point (STP) is a packet switch in an SS7 common-channel signaling network that routes call setup and database query messages, with voice traffic not passing through it.

Signal velocity

Signal velocity is the speed at which usable information travels through a medium, shown by Sommerfeld and Brillouin in 1914 never to exceed the speed of light.

Signal-averaged ECG

Signal-averaged ECG (SAECG), also called high-resolution ECG, detects ventricular late potentials via beat averaging; used for post-infarction arrhythmia risk stratification, with high negative but low positive predictive value.

Signal-flow graph

A signal-flow graph is a directed graph representing linear algebraic equations, introduced by Samuel J. Mason at MIT in 1953 and used in control systems.

Oct 20, 2026

Signal-recognition particle receptor FtsY

FtsY (Filamentation temperature sensitive X) is the single-subunit SRP receptor of bacteria and archaea, a membrane-associated GTPase homologous to eukaryotic SRα that delivers SRP-bound ribosomes to the SecYEG translocon.

Signal-to-interference-plus-noise ratio balancing

Signal-to-interference-plus-noise ratio (SINR) balancing is an optimization approach in wireless communications that adjusts transmit powers and beamforming vectors so the worst-served user's SINR is maximized under power constraints.

Signal-to-leakage-and-noise ratio

The signal-to-leakage-and-noise ratio (SLNR) is a performance metric for designing transmit beamforming and precoding in multi-user MIMO wireless systems, where it serves as an alternative to the signal-to-interference-plus-noise ratio (SINR).

Signal-to-noise ratio

The signal-to-noise ratio (SNR or S/N) is the ratio of a desired signal's power to the background noise accompanying it, usually expressed on the decibel scale.

Signalfire

SignalFire is a data-driven San Francisco venture capital firm founded by Chris Farmer, investing from pre-seed through Series B with a focus on applied AI companies.

Signalfire Breakout

SignalFire Breakout is the growth-stage fund family of SignalFire, a San Francisco venture capital firm founded in 2013 by Chris Farmer, supplying follow-on capital to scaling portfolio companies.