I would use this method:-

import poser
import os
scene = poser.Scene()
for fig in scene.Figures():
    geomFile = os.path.split(fig.GeomFileName())[1]
    if geomFile == "blMilMan_m4b.obj":
        print "%s based on %s IS an M4 figure" % (fig.Name(),geomFile)
    else:
        print "%s based on %s IS NOT an M4 figure" % (fig.Name(),geomFile)