count_sg.py

import os
import re

num_sg = 0
num_files = 0
for root, _, fnames in os.walk('.'):
    for fname in fnames:
        if '.parse' in fname:
            with open(os.path.join(root, fname)) as f:
                s = f.read()
                num_sg += len(re.findall(r'\(\s*SG\b', s))
                num_files += 1
print('Examined %d files' %num_files)
print('Found %d instances of SG' %num_sg)

On OntoNotes:

$ python count_sg.py
Examined 13108 files
Found 0 instances of SG