It is quite possible that the design was printed on, it was not uncommon to use mass-produced glass by decorators in modern times... 1950s on. Not necessarily from the same country either.
If this is the case here, then the colours will be fired on, try and scratch gently the colour somewhere not too noticeable. If it flakes then it is likely hand painted by an owner. If fired the product of a decorator - which could only be identified from their catalogues!