Mum unhappy about article that is printed in big type (8*)
I believe the answer is:
Here is my best explanation:
'that is printed in big type' is the definition.
(a masthead displays the title of a newspaper)
'mum unhappy about article' is the subsidiary indication.
'mum' becomes 'ma' ('ma' can be a synonym of 'mum').
'unhappy' becomes 'sad' ('sad' can be a synonym of 'unhappy').
'about' is an insertion indicator.
'article' becomes 'the'.
'sad' going around 'the' is 'sthead'.
(Other definitions for masthead that I've seen before include "Printed newspaper details", "Newspaper title", "Title of a newspaper printed at the top of the front page", "Newspaper identity", "Title of a newspaper or magazine", "furthest point from sea", "Top of paper's front page", "One's right up the pole", "Name of paper at top of front page" and "Something in large type".)