The image on the cover of the book is based on a theme closely associated with the Sufism. It might look to us like a bishop’s mitre, but what it is a Sufi symbol representing is the footprint of Muhammad. You can find examples by searching for “al-na’alayn al-sharif” or “the prophets’s sandal.” Exotic muli-coloured versions are displayed in the front windows of some houses, sometimes lit like Christmas lights. The simple outline is used as a lapel pin, or a design on a prayercap or as part of a logo on a website. The latticed version of it appears in posters.
Some Sufi groups encourage men to wear brightly coloured turbans, often green, sometimes red but usually not yellow. You might see them on special occasions. Sufis following Turkish traditions may wear a turban wrapped around a tall brown hat.