The result of ls command will depend of umask.

g+s will set sgid to the file. Check [here][1] for more deep information about SUID SGID

so if your umask for example is 044 the result will be something like:

 -rw-r--r-- 1 romeo UsersGrp 0 Jan 31 20:58 deux
 -rw-r-Sr-- 1 romeo canard 0 Jan 31 20:58 un


 [1]: http://www.linuxnix.com/2011/12/suid-set-suid-linuxunix.html