It's the still to-date ruling Alawite dynasty that first introduced the red flag. Both the royal banner and merchant ensign were plain red, while the war ensign displayed a a border of red and white triangles on an also red background. The white design in its center was commonly misinterpreted in Europe as tailor’s scissors --or two crossed scimitars as closest, when it actually was the two-bladed sword of Ali, or "zulfiqar".
Source: Flags of The World (FOTW) website:Morocco Historical Flags (from 1062 to 1912)
Sizes: ensign W12 x L18 mm, mast flags W8 x L12 mm, jack W6 x L9 mm, pennant W4 x L48 mm.