Steve is right, no focus peaking à la Sony et al.
But some may find this info useful as a tethered studio solution with (or without?) the use of a Sinar p-MF-L.
If you go to this page:
http://www.sinar.ch/en/category/products/cameras/p-mf-l/
and download the PDF, you can read the following:
The Leica S functions are fully integrated into the capturing software Sinar CaptureFlow and therefore can be conveniently controlled from the computer. Therefore, the Sinar p-MF-L can also be easily operated when shooting from higher positions. In the live image, Sinar CaptureFlow features a sharpness indicator for fast and precise focusing.
Yes, this means that if you manually focus the lens, you have a graph that indicates the level of contrast onscreen, in addition to the visual view itself. It doesn't overlay the image, it's a separate tool that shows a higher level of contrast depending on what part of the image you're viewing.
Edit: I don't know what live view capability they are referring to with a Leica S...
Steve Hendrix
Capture Integration