The only time I've noticed a quest actually tell me that it has changed my faction is when a particular quest sets the faction to something. An example is the newbie cleric quest, when giving advice in the temple, how you respond sets your alignment, and does not refer to what your alignment may have been before. (I could be wrong here, but I'm just going off what I've seen). Another example I can think of is when setting alignment with the main quest interview. This also sets alignment, and does not just give you a bump in any direction.
Most quests, however, just give a bump and don't say anything. For example, Grimble has done every evil thing possible, and gradually, his evilness has gone to greatly evil. Another example, Rehven has done much stealing and laundering of the proceeds, and his alignment has gradually shifted to deeply chaotic.