Hardcore shipbuilders have all probably heard of invisable thread for rigging their ships with. This is an advanced technique, akin to adding photoetch parts and ship's crew to their 1/350 and 1/700 scale work. For modelers working on one, another or both of our two builds, it is something that they might want to try. Invisable thread comes in 0.1mm and 0.2mm thickness, and in clear or a dark gray-green color. This latter removes the final task of having to use a permanent black sharpie marker to color the emplaced rigging with. Invisable thread can be purchased at any sewing supply center among the thread bobbins for sewing machines. If you have good references to work from, rigging can be done useing a combination of slow setting super glue to anchor each segment, fast setting super glue to tie off the end segment, and lots of patience. Remember to allow for catenaries in long segments and slack in the signal halyards.
I don't know of any 1/700 signal flags, but Revell used to include a sheet of flags with their large scale Battleships, Cruisers, other warships and liners. One thing about the positioning of flags on warships. Most drawings in instruction sheets repeatedly show the flag flown from the flagstaff on the stern. When ships are at anchor, this is correct, with the appropriate naval Jack flown from the flagstaff on the bow. Whenever a ship gets under-way, the national ensign is transfered to the mainmast, and prior to engageing an enemy, the normal ensign is replaced on the mainmast by the ship's battle-flag---usually something like 3 or 4 times the size of the normal under-way ensign.