Signal Meter.
Here is a photo of the signal meter in my HF transceiver:
Most transceivers will have some form of signal meter available, mine is a standard moving coil meter but others take the form of LCD Bargraphs. Both do the same job and are a multifunction indicating device.
You can see that the meter has two scales, the upper marked S ranges from 0 and is marked in odd numbers up to 9, the scale then changes to red and ranges from 0 to 60 and is marked in dB. This scale is red in actuality but the flash has rendered it Orange/Yellow, some flare as well from the perspex cover on the front of the transceiver.
This scale operates in receive mode and indicates the strength of the signal from 0 to 9 giving rise to the term "S points". For signals that are stronger than S9 they are then shown in dB gain over the maximum level of 9. There is an Internationally agreed system for reporting signals between stations which is known as the RST Reporting System. The abbreviation stands for (R) Readability - (S) Strength - (T) Tone. You can deduce from this that the system started life when all communication was by telegraph, the system was continued when telephony modes were developed. In telephony modes you only use the Readability and Strength to report the signal conditions.
The Wiki below shows how the system is used
Wiki - RST Code
The meter is shown in receive mode and is indicating a signal of Strength 6. the signal was completely readable so the report that would be sent would be 5-6
The bottom scale is marked PWR and has an additional scale in the middle marked ALC. This scale is used when transmitting and is dual purpose indicating transmitted power 0 - 150W. A pushbutton switch on the transceiver switches the metering between power and ALC which stands for Automatic Level Control. This scale is used to set the microphone gain (level of signal sent from the microphone), the scale shows the acceptable level of gain before introducing distortion to the signal. Once this is set correctly the meter can be reset to monitor transmitter output power using the toggle.