Sig lines often tend to be too wide for phones and take up too much space on small screens. That's why we did not have them on the DU3 mobile version and kept it that way for DU4.

Any device larger than a phone will show siglines, except for tablets in portrait (vertical) orientation which currently show a modified version of the mobile layout. I'm still tweaking that layout so we'll see if sig lines can be reintroduced there. I may also be able to get sig lines showing on phones in landscape (horizontal) orientation, but I'm not sure -- I'll have to see what it looks like.