To find the sign, get to the 10th checkpoint. When you jump through the window, try to stop on the bench and go as far as possible on it without falling off of the front. You should hear a second explosion. If not, you probably hit it already. Reverse back out of the window that you jumped through and you'll land in a small pit. Originally, the pit was filled with explosives, but triggering the second switch causes the explosives to detonate and additionally reveals the hidden sign.
As mentioned in the Middle Name: Danger info page, it is believed that the pattern is resemblant of the Fibonacci Pattern. The same shape can be seen in the first image to the right of the linked Wikipedia article. However, what's different about this pattern is that it also shows a pattern of dots underneath the Fibonacci Pattern.
The dots represent binary code, replacing the zeros and ones with dots and blank spaces. The binary, in zeros and ones, is 101010011110. This converts to 2718 in decimal, which happens to be the value of e, a mathematical constant. The relevance of e is still unknown. This code also converts to ©. Again, why?
This section is reserved for Confirmation/comments about this investigation. Investigations will remain open until advised by Redlynx that the final solution for each secret is found.