BackSlash is the administrative section of Slashcode. If you want to see the login on Slashdot, it's at http://slashdot.org/admin.pl. How do I know? Web server logs. When I submitted a story that was accepted, there was a hit from admin.pl to verify that I wasn't mirroring goatse.cx on my web site, or other such nastiness.
Update: Since I first wrote this, Slashcode has been updated. Users who visit admin.pl see either a generic login screen if not logged in, or their user page if logged in.
If you want to know more about BackSlash, download Slashcode and see for yourself.