When writing pin yin, should you use a question mark in sentences using "ma"? 你想吃饭吗？
   Ni xiang chi fan ma ?


Is it redundant to use ma and a question mark? Doesn't ma make it a question in of itself? I am unclear on the correct approach here.
For correctness, question marks are always required.

Are they redundant? Perhaps. If so, they are probably also redundant in English. (eg. "how are you." is clearly intended as a question even without the question mark)

"Ma" turns statements into questions. Think about "ma?" as being similar to "correct?" in English. (eg. "you like coffee, correct?")