Thanks.
The device is mounted on a PCB. Perhaps they tried to hide the markings, because they are weak. But with the right lighting, you can see them, as you see here:
I see ACS758 LCB-050B
I tried to obtain some characteristic regarding output voltage and current. This is what I got:
The typical sensitivity is 40 mV/A, but this device seems to have 57 mV/A.