sign function

[hbellafkir]

hi,

looking to models/predict/coco/predict_parallel.py script, you guys used np.sign as the sign function, but np.sign for x>0 returns 1 and for x<0 returns -1 and for x==0 returns 0. The sign function for hashing should return either {1, -1} or {1,0} and not {-1,1,0}