Those companies that marked their wares, and many of them did, were erratic in sometimes marking pieces and sometimes not marking pieces.
This shouldn't come as a surprise when you consider that the production period for many of these wares often covered between 50 to 100 years.
Minton china has been made in the Staffordshire region of England from 1796 to the present. Minton majolica is listed in this book in the Majolica category. ff3=4&toolid=10044&campid=5336649018&customid=minton&lgeo=1&mpre=
The firm became part of the Royal Doulton Tableware Group in 1968, but the wares continued to be marked Minton.
In 2009 the brand was bought by KPS Capital Partners of New York and became part of WWRD Holdings.