As I'm in Germany, this is a good time to take a break from my substantial activity in the local market to write a bit more on the Deutsche Bank handsignal used on many trading floors.
I've been told by a floor veteran that the Hitler's 'stache signal initially was used to indicate Dean Witter in the gold pit at the CME in the early 1980's because the desk manager for that brokerage was very difficult and was referred to as a Nazi. Eventually that signal became associated with Deutsche Bank but I don't know when/how that transition was made. The handsignal for Dean Witter eventually was mimicing being on the phone in reference to one of their marketing slogans.
As for the use associated with Deutsche Bank, the signal was certainly "unofficial" (not officially designated by the exchange) and used because someone on the floor started to indicate that firm w/the signal so it stuck. At the CME, it was the index and middle fingers held horizontally beneath the nose but evolved into just the index finger horizontally and a downward scratch motion as if Hitler was scratching his 'stache. LIFFE consistently had the two horizontal fingers from what I've been told. I've seen some use the same fingers vertically which is a more accurate representation of the mustache but it might be confusing with a quantity of 1 or such and thus wasn't widely accepted/used.
So why was this signal even used? The "official" designation for firms was to signal the three digit firm number, Deutsche Bank for example was 092 at the CME. Thus, it was a much short and efficient way to signal a memorable, albeit politically incorrect, hand signal than to indicate four signals, a house to indicate brokerage house and then the numbers 0, 9, and 2.
Could something else been used rather than the Hitler signal, of course but it stuck once someone started using it. If a signal was needed today, I'd suggest things such as references to Sprockets or the TechnoViking to reflect Germany.
The other German banks such as Commerzbank or Dresdner Bank were generally not large enough players on the trading floors to have specific signals applied to them.