You are probably right: this is a late Edo copy of or "homage" to Yamakichibei (specifically, to the nidai, who was a smith in the Yamakichibei atelier in the Momoyama and very early Edo Periods). The other possibility is that this is a post-Edo Period piece. It is certainly no earlier than 19th-century.
The rectangular hitsu-ana are not kantei points for the authentic Yamakichibei smiths: I can't recall seeing any genuine works with such hitsu-ana.
As for the motif, this is one associated with two of the smiths of this atelier---the nidai and one other tsubako (see attached photo for example of his work). I don't know that I have seen any explanation/identification of this motif that is confident or certain of what it is. I have seen it described as a katakana "e" character, but I am a bit skeptical of this.
As to the mei, since this is a piece having been made at least 200 years after the end of the actual Yamakichibei workshop, the signature of course cannot be "legitimate," if by this term you mean to reference one of the authentic tsubako of that workshop.
There are many other indicators in this tsuba that show it to be a very late copy/homage: the steel is nothing like actual Yamakichibei metal. The shape is not one used by the 16th/17th-century smiths. The rim is perfunctory and ho-hum (nidai Yamakichibei rims are sublimely excellent). The "amida-yasuri" are amateurish (compare to authentic nidai amida-yasuri in the photo below).
Hope this helps...