Well I'm going to post what I've figured out about this clue so hopefully someone else might be able to provide some more insight to it. As most people have probably figured out, the coin seems to most likely be located at the museum of science and industry. This was determined as N:TAS stands for Navy: Technology at Sea which is an exhibit at the museum. What also aids in knowing it is at the museum it the fact that we know the coin is in Chicago and that the picture shown is a U-boat periscope. (The full picture can be viewed here
http://www.mikekemble.com/ww2/subs/periscope.JPG). Therefore this would imply that the coin is on the U-505 in the museum which is the only U-boat in Chicago. However, this is where things throw me for a loop. The U-505 exhibit and N:TAS exhibit are on two separate floors, though they are right above each other. So this brings to question, which exhibit is it actually in? If you follow the riddle and find N:TAS, then whats the point of the picture if it represents a different exhibit? For those of you that have been in the N:TAS exhibit, there are two periscopes in a mock submarine in it, but these periscopes are for a US submarine, not a U-boat like the pictures show. (The periscopes show the streets outside the museum). So I went to go check out the U-505 periscope, even though its not in the N:TAS exhibit. The only problem with this is the U-505 periscope isn't on the U-boat and is lying on its side outside of the boat in a case, so that theory was a dead end. Ok, so at this point I have only explained the picture and the first line of the riddle. The second line of the riddle about "playing a game of eye spy with arrows" most likely relates to the fact that the room with the staircase that leads up to the N:TAS and also leads to the U-505 exhibit is connected also by an exhibit called Eye Spy. I figure this must be related because the game Eye spy is actually spelled "I Spy", not Eye Spy, so why spell it incorrectly unless there is a reason. So I took a look inside the Eye Spy Exhibit to which I found half the exhibits inside have been taken down including one called Under the Sea and another one relating to clocks. Ok, so another dead end in here. Therefore this brings us to what it means by play eye spy with arrows. The only arrows that you can see from the Eye Spy exhibit are the ones for the sign that says N:TAS with an arrow pointing up and the one for U505 right below it with and arrow pointing left. So I figured I'd follow the arrows until I saw something that looked like a rainbow (either in color or in shape). In the U-505 of hallway you see a sunset right away when you look down the hallway with two guys sitting on a piece of wood in the ocean. Right to the left of this display around the corner on a wall are posters that tell the story of U-505, the interesting thing about this wall is it zigzags in and out with a poster on each zig. So I followed this to the last poster and looked behind it, nothing there. So I backtracked back to the sign with arrows and went upstairs to the N:TAS exhibit and found a giant painted topographical map of Mars at the top of the stars with every color of the rainbow on it. About 20 feet to the right of it starts a hallway that sort of seems to have displays on the left walls sticking out of it like a zigzag. If you follow this you end up in a room that is called Inventions: Ordinary or Extraordinary, yet after searching this room, still empty handed. At this point in time I aimlessly searched in these three exhibits for zigzag shaped things and after searching all walls that jutted in and out and the tops and bottoms of all staircases (which are also zigzagged), I still had nothing. Therefore I must concede defeat to this puzzle until I get another clue or until someone can determine where I messed up which is most likely in what the rainbow shaped object is or what the zigzag is. I am fairly confident I am in the right place when searching. I also have pictures of everything I described above, but I will not share them on here as I do not want people who did not pay to enter the museum to be able to have them. If you would like to see what I'm talking about then you will have to visit the museum yourself and pay the admission and parking fees. (I'm not trying to be rude, It just cost me $27 dollars between admission and parking for the museum not counting gas). However, if you would like to seriously aid in helping me find the hidden coin and have thoughts about the rainbow object or zigzag, PM me and I will consider sharing the pictures with you so you can help. (This offer is really more for people who just like solving the riddles and don't care about the coin or ISIS).