The above sign ‘Big Sushi’ is grammatically incorrect. Many adjectives of size; such as the words ‘big’ and ‘small’, cannot be used with uncountable nouns. This is the case as many uncountable nouns are considered to be formless, thereby making them difficult to assign a size to. For the same reason, it would also be incorrect to say that one:
speaks big or small English
plays big or small soccer
has big or small love.