And a bit extended:

from collections import namedtuple

sc = poser.Scene()
ac = sc.CurrentActor()
geom = ac.Geometry()

VERT_REC = namedtuple("VERT", "X Y Z idx")
verts = [VERT_REC(v.X(), v.Y(), v.Z(), i) for i, v in enumerate(geom.Vertices())]
_min, _max = min(verts), max(verts)

print "Min vert value in", ac.Name(), "=", _min
print "Max vert value in", ac.Name(), "=", _max

left_verts = [v for v in verts if v.X < 0]
right_verts = [v for v in verts if v.X > 0]
zeros = len(verts) - len(left_verts) - len(right_verts)

if zeros == 0:
    print "There is no zeropoint in X."
else:
    print zeros, "Zero points"

# now with tolerance
tolerance = 0.001
left_verts = [v for v in verts if v.X <= -tolerance]
right_verts = [v for v in verts if v.X >= tolerance]
zeros = len(verts) - len(left_verts) - len(right_verts)

if zeros == 0:
    print "There is no point between", -tolerance, "and", tolerance
else:
    print zeros, "Zero points with tolerance +/-{}".format(tolerance)

---