Back to the tow bar.
Its easy not to see the tow bar after disconnect. At HERG yesterday the tug drove off almost immediately the a/c stopped durring pushback, without the towbar! A small baggage tug appeared & took said bar in opposite direction. When ground staff gave wave off with pin, no tug(s) or towbars to be seen. If your busy monitoring your engine start proceedures & a little baggage truck departs right with tow bar it can be very hard to spot from "the office" even in a 738. You rely on your team, sop's & experience. Often its the experience that is the final saftey net, with sop's giving you a supperb foundation.
Jumbo.