Linux – What does the + mean in the output of “ls -l”

You cannot do this; the initial owner is always the object's creator.

What you can do is set the default ACLs to automatically allow read/write to everyone:

setfacl -m default:u::rwx,default:g::rwx,default:o::rwx /public/all

Also optionally set a default group:

chown :nobody /public/all
chmod g+s /public/all

However, none of these will prevent the owner from changing the permissions later.

An alternative solution is to monitor the directory with inotify (using incron) and automatically run chown on creation. Put this to incrontab:

/public/all IN_CREATE chown nobody:nobody $@/$#; chmod 0666 $@/$#

Your ls seems to have an alias to ls -F. It shows the filetype:

* for executable
/ for directory
@ for symlink
| for fifo
= for socket