Presences are not visible with the eye, they can only be felt.
One Presence resides in the cabin of the Lady Luck. It is a femine entity who is known to only respect those who she fears may do her harm. Passengers cannot allow themselves to be intimidated. She spoke to Seth Sorenson when the Knights of the Dawn were going to Shoreless Isle. Seth managed to persuade her to take them there using his sword, Vasilis.