Originally Posted by sewbizgirl
Y'all are right-- It's an inkwell. I have read a vintage ad for this model cabinet (somewhere online!) and it was sold as a dual-purpose sewing cabinet and writing desk. There is also a paper tray installed on the right side, behind the door and above the two big drawers. This tray does not pull out like the drawers, but has a cutout where you can reach in and pull out a sheet of writing paper!
There are variations of this desk. I've seen it in at least three colors, and the one I own doesn't have the inkwell, but rather a six-pin rack for thread spools in the inkwell location. These cabinets came with only the 201 or the 15 installed in them. They are wired and have their own foot controller built into the cabinet.
This is the "Art Deco" cabinet...
I have this cabinet as well, it was purchased with a singer mocha 301 by the original owner. I have the 6 pin thread storage in mine, but if you go over to ISMACS, Gordon has an entire page devoted to the Singer cabinets. Mine has the knee controller built in. Someone painted mine a blech brown, but I will be stripping it at some point when it's not 19 degrees outside (and snowing even!) I have the matching stool to go with it too.