A manual valve is attached to the radiator body on which it is placed whereas a thermostatic valve can easily be removed from it.
It is suggested not to disassemble a manual valve without the intervention of a professional as this may require draining your hydraulic system.
A thermostatic radiator valve can be easily removed from the body on which it is placed, without the need to purge your hydraulic system. It is generally graduated from 1 to 6.
How to recognize your radiator valve:
Manual valve
Thermostatic valve