mkdir -pm2750 foo/bar
$ ls -lh
total 4.0K
drwxrwxr-x 3 hena hena 4.0K 2012-04-27 14:30 foo
$ ls -lh foo/
total 4.0K
drwxr-s--- 2 hena hena 4.0K 2012-04-27 14:30 bar