NO POP means not populated (i.e. the space on the PCB is there, but there's no component). In this case you'd install nothing.
Zero-ohm resistors are used just for jumpers (so the same machinery can be used for jumpers and actual resistors). In this case you could use a jumper or a wire.
It's a flexible connection of some kind. In this drawing, it is likely to represent a trailing or reeling cable (I will explain this a bit more below.)
Supporting my claim - from AS1102.3 Graphical symbols for electrotechnical documentation - Part 103: Conductors and connecting devices, we have:
Note AS1102 is based on IEC 617 Graphical symbols for diagrams.
Contrast the symbol for a jumper ("connecting link"), also from AS1102.3, and a fuse, from AS1102.7.
What's a trailing cable?
A trailing or reeling cable is used to power mobile equipment, i.e. a mobile drilling rig, or mobile substation.
In this application, I think the 'sub-sea' transformer is in some kind of waterproof container, connected to the surface supply by trailing cables. Flexibility is required for the transformer to be moved around, or to move with the water currents.
Note that trailing cables are a special breed, not like regular cables. See Olex catalogue for trailing and reeling cables. Generally these cables are much more flexible than normal cables, are designed to withstand cars running over them, etc. There are also special protection features to detect if the cable has been damaged - these aren't required for normal cables which spend most of their life living in a protected environment, i.e. conduits.
Best Answer
Most likely the 'K' position indicates the decimal point position.
So, $$ 5K1 \equiv 5.1k\Omega $$ $$ 3K9 \equiv 3.9k\Omega $$
In the same vein as: $$ 3V3 \equiv 3.3V $$
Just a way to save characters/area, and avoids the issue of the decimal point fading out when printing/copying/faxing.