A : Sometimes they are noticed—and want to be. They may take on a form that is normal for them in their own dimension, but very much not normal in the environment they are visiting, thereby allowing themselves to be noticed.
They would do this if their intention is to let those living outside of their dimension know that (a) they exist, (b) they are present, and (c) they mean no harm, and have only come to help.
If a Highly Evolved Being feels that being seen in its own physical form would shock or dismay and rally unnecessary defenses, thereby working against its very reason for moving from the metaphysical to the physical in a location outside of its dimension in the first place (which is to help, not frighten),
it will take on the form of the beings it seeks to assist, and will do so in a way that allows it to meld into another civilization without making its presence disruptive, dismaying, disturbing, startling, or alarming in any way.
A : It will embody at the earliest possible moment in the life cycle of the beings it seeks to help, moving through the same developmental passage of every entity in that civilization.