I have GY-471 in a DC motor circuit to measure current. Everything works almost as expected. I have also put an ACS712 in the same circuit.
The ACS712 shows bidirectional current flow by having a signal either above or below 512 when read on an analog pin. This works as expected with the current being drawn, greater than 512) by the motor when accelerating and when on the overrun with power removed it works as a generator and signals are less than 512.
The MAX471 on the GY-471 board shows the same shape of signal when the motor is being powered (it is a 0-3A device and the range is 0-1023) so the signals are greater but the same shape. When the motor goes into overrun the signal is still positive and the shape is the mirror image of the ACS712. This is totally as expected.
What is supposed to happen is the SIGN pin goes from high to low depending upon the current flow. In order to get the pin to behave the MAXIM documentation says this pin should be pulled high with a 100K resistor.
I have tried a range of resistors from 10K to 300K and this pin does change from high to low but it is not in agreement with the current flow 
It 'twitches' one way as the voltage is ramped up and the current starts to flow and it 'twitches' again as the voltage is killed and the motor goes into overrun again.
Has anyone made the SIGN pin work please. No joy on the internet as nobody has uses the SIGN pin.
Cheers Alan