docs/esp32: Mention Signal in GPIO section of quickref.
@@ -171,6 +171,10 @@ Notes:
* The pull value of some pins can be set to ``Pin.PULL_HOLD`` to reduce power
consumption during deepsleep.
+There's a higher-level abstraction :ref:`machine.Signal <machine.Signal>`
+which can be used to invert a pin. Useful for illuminating active-low LEDs
+using ``on()`` or ``value(1)``.
+
UART (serial bus)
-----------------
