An early gilt mark, “made by Meizan”, found on a small number of early pieces, including the Osaka Museum of History charger with a white elephant and Chinese children (before about 1890).
“Meizan sei” (明山製), early studio mark

Authentic features
Documented on the Osaka Museum of History charger, a beaker sold at Bonhams London in 2014 ("signed on a gilt seal Meizan sei") and a covered jar sold at Bonhams Paris in 2025.
Common forgery flags
The separate Kanazawa Meizan also signed "Meizan sei". Attribution depends on quality and style, not the mark alone.