The term hilye or hilya (Arabic حلية meaning "adornment", "attribute", "description" or "appearance") is a calligraphic physical description of the Holy Prophet Muhammad (peace be upon him). It is common belief, especially during the Ottoman times, that that reading and possessing Prophet Muhammad's (peace be upon him) description protects the person from trouble in this world and the next, and as such it became customary to carry such descriptions in a breast pocket or to hang one on a wall of the home.
Hilye, both as the literary genre and as the graphic art form, originates from shama'il, the study of Prophet Muhammad's (peace be upon him) appearance and character. The best source on this subject is considered to be Imam Tirmidhi's al-Shama'il al-Muhamadiyyah wa al-Khasa'il al-Mustafawiyyah ("The Sublime Characteristics of Muhammad"). The acceptance and influence of this work has led to the use of the term "shama'il" (appearance) to mean Prophet Muhammad's (peace be upon him) fine morals and unique physical beauty. As they contained hadiths describing Prophet Muhammad's (peace be upon him) spirit and physique, the shama'il has been the source of hilye.
The best known and accepted of these hadith are attributed to his Sayyidina Ali, the prophet's cousin and son-in-law. The description of Prophet Muhammad by Ali, according to Tirmidhi, contained in the hilye, is as follows:
[It is related] from ‘Ali (may God be pleased with him) that when he described the attributes of the Prophet (may prayers to God and peace be upon him), he said: "He was not too tall, nor was he too short, he was of medium height amongst the nation. His hair was not short and curly, nor was it lank, it would hang down in waves. His face was not overly plump, nor was it fleshy, yet it was somewhat circular. His complexion was rosy white. His eyes were large and black, and his eyelashes were long. He was large-boned and broadshouldered. His torso was hairless except for a thin line that stretched down his chest to his belly. His hands and feet were rather large. When he walked, he would lean forward as if going down a slope. When he looked at someone, he would turn his entire body towards him. Between his two shoulders was the Seal of Prophethood, and he was the last of the prophets."
It is also reported that Sayyidina Ali said: A short time before Muhammad's death, when his crying daughter Fatima said to him: "Ya Rasul-Allah, I will not be able to see your face any more!" Muhammad commanded, "Ya Ali, write down my appearance, for seeing my qualities is like seeing myself."
More information about the hilye can be read here http://www.zakariya.net/resources/hilye.pdf