I like to know:
1- what the equal sign after the V mean, the upper part of that sign is solid line.
Power supply labels indicate, among other things, allowed input voltage and designed output voltage and current.
The symbol like a reversed S on its side means "alternating current". So the input voltage can be anywhere from 100 to 240 volts AC, and the frequency can be 50 or 60 Hz.
As for the output, the symbol with a lower dashed line and an upper solid one means "direct current". So it will supply 12 volts DC at 4.16 Amps.
2- there is no indication of polarity. Why?
Many pieces of equipment use a general purpose type power supply, with a standard connector that has one inner and one outer contact. These can have the polarity either way around so you see an informative label.
However as you said...
The power input on the monitor is round and has 4 little pin.
...this monitor has a power supply made specially for it, with a 4 pin connector that cannot be inserted into another piece of equipment with a standard DC connector. Thus there is no need for polarity marking. The user does not need to know what polarity the pins are. The user is not advised to attempt servicing.
