Last I recall it didn't, which kind of soured me on it - in an ideal world every sync operation would be prefaced with "send a backup to one of my backup endpoints first".
Backing up your filesystem can and really should be part of an entirely different process. Let syncthing focus on syncing. Get CrashPlan, rsync, or some other process going on your filesystem for backups. Unless you are hoping for backing up every single version of your documents.
(But Syncthing is intended for file syncing, not backup.)