Oddly enough, for all the Ash Wednesday Masses and distribution services I've attended in my life, I have no conscious memory of ever seeing a priest with ashes on his head ... probably because I wasn't looking for it. But, in case you were wondering, not even the Pope escapes this ritual:
"Remember, O man, that 'you are dust, and to dust you shall return'"(Gen 3:19). Even if you're the Pope.