Imposition of Ashes - where in Catholicism is it commonly practiced? Since I learned of this practice, I thought that placing ashes on Ash Wednesday is practiced worldwide, at least within the Roman Catholic Church. But now I have been to a Mass (on the first Lent Sunday, when ashes may be placed for those who didn't receive this sacramental on Ash Wednesday) attended by some Portuguese people. They seemed puzzled when they saw the priest placing ashes on other worshipers - they apparently didn't know the practice.

I checked the Czech (I'm Czech) and English Wikipedias, and they both highlight the practice of placing ashes. I don't speak Portuguese, but Portuguese Wikipedia has no ashes-themed picture and from the little I understand, it seems that this practice is not even mentioned there. Anyway, Portugal is unlikely to be the only country not observing imposition of ashes. English Wikipedia gives a list of churches observing Ash Wednesday, but not one of countries where the practice of placing ashes is (or is not) observed in the Roman Catholic Church. Is there any such list?
I believe that the imposition of ashes is universal within the Roman Catholic Church.  The practice was "made official" in a 1091 decree of the Council of Benevento, which states:


  "on Ash Wednesday everyone, clergy and laity, men and women, will receive ashes"1


Before that, the practice was done in private, dating back many centuries, and probably in some church services since at least the 8th century. 

What is not universal is how the ashes are applied. A 1988 circular letter simply states: 


  On the Wednesday before the first Sunday of Lent, the faithful receive the ashes, thus entering into the time established for the purification of their souls...  The blessing and imposition of ashes should take place either in the Mass or outside of the Mass. In the latter case, it is to be part of a liturgy of the word and conclude with the prayer of the faithful.2


Thus individual churches may administer the ashes in different ways.  Traditionally, men received ashes sprinkled on the crown of head, while women received them in the form of a sign of the cross on the forehead.  In English-speaking countries today, it is common to mix the ashes with water (to make them stick better) and make a sign of the cross, while in other places a cross is made without any water.  In Rome, the traditional sprinkling practice is still used.  Apparently some churches now use a "stamp" to impose the ashes. (See also this article which states: "There are no set rules regarding this, and it largely depends on local custom.")

Turning to the specific example cited, the Portugese Wikipedia may have failed to mention the practice when the question was originally asked, but it now says:


  Missas são realizadas tradicionalmente nesse dia nas quais os participantes são abençoados com cinzas pelo padre que preside à cerimónia. O padre marca a testa de cada celebrante com cinzas, deixando uma marca que o cristão normalmente deixa em sua testa até ao pôr do sol, antes de lavá-la. ("Masses are traditionally held on that day [Ash Wednesday] in which participants are blessed with ashes by the priest who presides over the ceremony. The priest marks the forehead of each celebrant with ashes, leaving a mark that the Christian usually leaves on his forehead to the sunset, before washing it.")


The Portuguese people in Czech service described in the question were presumably confused either by the method by which the ashes were applied or by the fact it was being done on a Sunday (as suggested by a commenter).  I was not able to find any evidence of Roman Catholic Churches that don't physically administer ashed in Portugal or anywhere else.