So here's the "name" at the top of the odd tombstone painted on the wall in the back stairwell. It's not a name at all... at least, not one name. It's a portmanteau, two names smushed together, like Bennifer.

The names on the bottom half of the tombstone are Rebecca and Jenni. The names on the mailbox for that apartment are also Rebecca and Jenni. And their last names put together, make "Spinkell."

Case closed. Stupid mystery solved.