That’s a generic “Xiang Gang Jia Gong” mark (香港加工) used on export ware which is not attributable to a specific maker. The mark is read right-to-left for each of the two rows. My understanding is that it translates to “Hong Kong Final Process” and means that the decoration was added in Hong Kong, but the original fired porcelain blanks were produced elsewhere and could be either Chinese or Japanese. Our esteemed member “Yang Hao” can probably comment on whether I have the translation correct.
That mark is commonly seen on plates and dishes from the 1960s and 1970s when Hong Kong was under British administration.
PS: if you go a-Googling, you may come across this, described as “vintage Mizusashi Japanese” (and over-priced despite the “20% off” in my opinion):
It has the same generic Hong Kong mark as yours, shown upside down by the seller. I think the seller has found another piece of porcelain with similar decoration and that generic mark on the net labelled as “Mizusashi”, put two and two together, and come up with five.
There has been no Oriental porcelain producer called “Mizusashi” as far as I know. It’s the traditional name for the cold water vessel used in Japanese tea ceremonies and doesn’t have a dish form… it’s a taller pot-like vessel, although it is sometimes rested on a shallow dish.
Both dishes seem to have identical wooden display stands, so I would think they were made purely for decorative purposes.