Mimic using a snap camera by using index finger to push down as thumb holds imaginary camera.
Fuji wasn't just used as the name of a bank, it was also the same name of a large camera/film producer from Japan.
The ability to recognize all market participants was what made open outcry trading transparent and from this, signals were developed for the larger brokerages and for some large local traders. In cases where a more universal signal was never developed, their hand signal in the pit would simply be their three digit firm number