This is just from my experience, so I don\'t know if it is across the board. Typically, I can sense if a person has an aptitude for telepathy/empathy or other perception based \"psionic arts\" (using the word in the same context that you used it) by psionically observing them (I think the term scan has too many implications and can be somewhat intrusive). In my experiences there is often times a weird type of \"awareness\" around them. How do I explain it? Like a weird mechanism that is kind of like a node that extends outward and then goes inward into themselves... like an input function.
I simply focus on the person and lightly observe them, but without \"touching\" them. I find psionic contact to be VERY intimate and it slightly freaks me out, so it is rare that I do any form of linking what so ever! It is equivalent to standing to the side and watching a person instead of going up to them and touching all over them and asking questions. What I have found with perception based things, like I said before, there is typically the presence of an additional awareness and a weird type of... what is the word that I am looking for (it is hard for me to translate these things into words) node. Typically with non psions, there is no presence of that. I hate to use this comparison, but it would be as if you were physically looking at two groups of people. One would have eyes the other wouldn\'t. That is kind of how it is, for me. Normally it is a type of sensitivity that I can sense that extends outward to their surroundings and then inward.
Typically, from what I have sensed, people who are good with PK generally have a harder more intense feel. Normally it is a combination of that awareness I mentioned earlier combined with a weird type of... what is the word... I don\'t want to use their weird, but it is the only one that comes to mind, output affect that is typically rougher in texture. A lot of times, from what I have observed, it is a weird extension of the node I had mentioned before hand, but with a rougher feel.
I spend/have spent a lot of time around psions with different areas of forte\'s and non psions, so I kind have learned to make comparison\'s between what I sense and how it feels and what it could possibly mean and so on and so forth. That is from my interpretation of the information, however, and I am not saying that it applies across the board. Oh, and people who are into psionics normally show up \"louder\" on my radar.
I can visually see my own creations with psi energy and the creation of other\'s with my eyes (not indirectly through \"scan\" type things), but I have no idea why or how. It is just something that I have had since I was little. I can\'t explain to you how that works, LOL.