XXL Detective Puzzle

Who has not at one time or another felt like a detective and gone searching for clues? This puzzle makes it easier for us to find out about things, to discover, look closely and investigate.

The red plexiglass in the middle can be removed and put onto the areas which appear red and "invisible". Take a close look what you can see now!! Further more, the edge is scattered with symbols. Can you find all of them on the puzzle?