A speaker with a cross or slash, silencing audio output.
A speaker cone marked with a cross or a diagonal stroke means sound is off. Whether pressing it mutes or unmutes is genuinely ambiguous, because the icon may show either the current state or the action.
Indicates that audio output is silenced, or acts as the control that silences it.
Contexts: Software
Whether the icon reports the current state or the action it will perform is not settled between platforms, which is why users press it to find out.
Contexts: Software
A small square with a trapezium flaring to its right, forming a speaker seen side on, with a diagonal cross or single stroke drawn across it.
Both are used in software contexts.