Hahah.. I was waiting to see how long till someone posted... I have made three trips to the Science of INdustry - so I'll give you this:
I have searched all over oustide... I have searched all over the UBOAT.. I even got a security guard named Johnny to help me... he gave me a private tour of the UBOAT and we searched everywhere on that thing.
There is a periscope on DISPLAY to the right side of the UBOAT... you can actually look through IT.. when you do, you can see the Torpedo's display case, which is a circle, except you can only see HALF The circle when looking through it and lining up the arrows (Rainbow Like) .. Then I followed the stairs behind that (Zig Zag), nothing there... then I followed the railing that zig zags around the UBOAT, nothing there.. I as well have pictures.
So... My thoughts are - it must be in the NTAS when you look out the periscope. I have had two people on cell phones trying to line up rainbow like objects. My first thought was the Flag... for unknown reasons.. .then I tried lining up everything. I walked all around the museum, even the side that is closed off, and checked every possible zig zag I could think of... Nothing.
So best of luck to you. If you would like to meet up sometime and try and put what we have found together, I would be willing to do that. I'm actually going to be in Chicago again for a bachelor party Sat night (I live 2 hours away), so Sunday I could stop and help look...
I already bought my isis on my last (third) trip to the museum.. so hopefully any insight I have given helps.
I'm sure it has to be something outside the museum.. .because everywhere in the Naval part has been searched.
OH - one more thing... the third periscope in the NTAS (the one showing the next room) , if you look threw it the lights above appear to be a prism... and on the other side of the wall there is an electrical box with a logo showing the ELECTRIC WARNING Sign (zig zag).. dont bother with this either... and the electrical tape covering up the box it leads to... opening that will just possibly electricute you.. but definitely get security asking questions about what in the hell you are doing