Either case, if it was me, the most LOGICAL way to travel through any particular time/space would be to activate the 5th (in/out) dimension, which means that one would have to take different energy forms..
In other words, traveling in 3D would not be the most effective way to reach very long distances, like light years!
As such, any 5th dimension traveling object would seem "cloaked" to us as it tries to re-take form into the physical dimension..
Even if one was traveling from one particular space/time point in the physical dimension, to another space/time point in the physical dimension, through the 5th dimension, then the particular object that was traveling would have to change energy forms..
As such, if one is measuring energy at different frequencies, one may detect infra-red and other frequencies, but not necessarily visible light frequencies, unless, of course, the object takes full shape/form in the physical dimension..
But, if I was the one designing a UFO, I would try to maintain it in a cloaked format for as long as necessary to avoid hostile behavior one way or the other. Just simple logic...
The Invisible Universe