Charles Ellicott Commentary Leviticus 8:12

"And he poured of the anointing oil upon Aaron`s head, and anointed him, to sanctify him." — Leviticus 8:12 (ASV)

And he poured of the anointing oil upon Aaron’s head. —In the anointing of Aaron, the oil was poured upon his head (Exodus 29:7; Psalms 133:2). This profuse pouring of oil was repeated at the consecration of every successor to the high-priesthood, while the common priests were simply anointed, or were simply marked with the finger on the forehead on their first installation, and this anointing descended with them for all future time . Tradition informs us that during the Second Temple, the person who anointed the high priest first threw the oil upon his head, and then drew with his finger the sign of the letter Caph, being the initial of Cohen, i.e., priest, between the eyebrows of the newly-consecrated pontiff.