Plain as a pikestaff
‘Plain as a pikestaff’ means obvious or very clear and dates from the mid-1500s, before this, the expression was actually ‘plain as a pack staff’, which was the staff or pole on which a pedlar tied his pack. By the mid-1500s, it changed to pikestaff for no known reason. The association of a pack staff or a pikestaff to plainness is obscure except for the obvious alliteration. As an expression, it has largely been replaced by ‘plain as day’ or ‘plain as the nose on one’s face’.