This is a signal that the on-board diagnostic system has detected a malfunction in the emission, ignition or combustion systems of the vehicle. It could be something as simple as a loose plug or something as serious as a bad catalytic converter, so you should not ignore it.
All modern cars have a on-board diagnostic that is supposed to detect engine-related issues that affect emission control systems. The engine control light (typically with the shape of a yellow or orange engine) should light up for a few seconds each time the engine starts, along with other spies. If it remains on, it means there is a problem to be detected and resolved.
If the engine control lamp blinks, it usually indicates a mere ignition or another serious problem, which should be tackled quickly by bringing the car to a mechanic. Ignoring this blinking light, in fact, increases the likelihood of additional problems, including the damaging of the expensive catalytic converter (whose replacement costs more than 1,000 euros in some cars).
If the warning light does not blink, the fuel tank cap must first be tightened before running the engine, as a simple loose plug may sometimes trigger a warning. You see if the light goes off after several engine starts the next day or so. Even replacing a wasted fuel cap that does not seal completely could solve the problem.
If all this does not work and the light remains on, the mechanic will need to diagnose the problem by electronically connecting to a special connector beneath the dashboard to read the diagnostic codes that will help isolate what triggered the spy, such as for instance a bad spark or connection with the oxygen sensor.
Even if the vehicle seems to have a good performance, it is a bad idea to ignore the engine warning light. Something is wrong, and is going to get worse. Also, if you are living in an area where vehicles need to pass regular emissions tests, an engine warning light usually means that the vehicle will not pass the emission test, so please contact the mechanic as soon as possible.