Tofukuji used at least 15 stamps in the course of his career, plus his signature. Discrepancies in the stamp are often one of the easiest ways to spot a forgery.
Some things to look for in comparing stamps for forgeries are discrepancies in character, depth, stamp edge, and relative size.
One of the most recognized and forged marks in the world. Tofukuji used two different stamps of the Trident leaf style, the second is less broad and more rounded at both the top and tip of the bottom leaf, the left leaf dips down slightly, and has less ridge definition. The letters are larger relative to the leaf size as well.
The above three impressions are differing Tofukuji stamps, of the same in line vertical style. One is boxy and shows a straight line impression around the edges, while the other have ovate edges. In all Tofukuji used 4 stamps of this style, making forgeries sometimes difficult to detect. Note the depth of the impressions and stamp edge shape, forgeries are often pressed to deep and have different size and/or shaped edges.
I hope this glimpse at Tofukuji signatures and stamps has been informative. There are many forgeries, both here and in Japan. Many a collector has been taken in by a good forgery. A keen eye for details and a strong background in the material are indispensible in spotting the difference.