This is an amazing (but very proper powerpoint presentation about it):

However this is the official speak for how to recognise it and what it is:

CRPS I /RSD is a diagnostic consideration for patients who have pain (moderate to severe) that is disproportionate to any inciting event (sprain, fracture,etc.) and has some of the following characteristics: Pain is described as deep, aching, cold, burning, and/or increased skin sensitivity. The presence of an initiating noxious event (sprain, fracture, etc.), continuing pain (moderate to severe) associated with allodynia or hyperalgesia. The pain is disproportionate to any inciting event. Abnormal swelling in the affected part, Abnormal hair or nail growth, Abnormal skin color changes, Abnormal skin temperature (greater than 1°C assemtry), abnormal sweating. Limited range of movement, weakness, or other motor disorders (Paralysis, dystonia, etc) CRPS I /RSD is excluded by the existence of conditions that would otherwise account for the degree of pain and dysfunction.