Objection 1. It would seem that this sacrament imprints a character. For a character is a distinctive sign. Now just as one who is baptized is distinguished from one who is not so is one who is anointed, from one who is not. Therefore, just as Baptism imprints a character so does Extreme Unction.
Objection 2. Further, there is an anointing in the sacraments or order and Confirmation, as there is in this sacrament. But a character is imprinted in those sacraments. Therefore a character is imprinted in this one also.
Objection 3. Further, every sacrament contains something that is a reality only, something that is a sacrament only, and something that is both reality and sacrament. Now nothing in this sacrament can be assigned as both reality and sacrament except a character. Therefore in this sacrament also, a character is imprinted.
On the contrary, No sacrament that imprints a character is repeated. But this sacrament is repeated as we shall state further on (33). Therefore it does not imprint a character.
Further, a sacramental character causes a distinction among those who are in the present Church. But Extreme Unction is given to one who is departing from the present Church. Therefore it does not imprint a character.
I answer that, A character is not imprinted except in those sacraments whereby man is deputed to some sacred duty. Now this sacrament is for no other purpose than a remedy, and man is not deputed thereby to do or receive anything holy. Therefore it does not imprint a character.
Reply to Objection 1. A character marks a distinction of. states with regard to duties which have to be performed in the Church, a distinction which a man does not receive by being anointed.
Reply to Objection 2. The unction of orders and Confirmation, is the unction of consecration whereby a man is deputed to some sacred duty, whereas this unction is remedial. Hence the comparison fails.
Reply to Objection 3. In this sacrament, that which is both reality and sacrament is not a character, but a certain inward devotion which is a kind of spiritual anointing.
Source: Summa Theologica (New Advent)