There are many excellent descriptions of the ISTp (Sensing Logical Introvert) out there, so I'll try to refrain from a rehash of all of those articles. But I'd like to take this opportunity to provide some of my personal observations of the type and how to know if you're in the presence of one.
- The ISTp is calm. Weirdly calm. Above everything else, the ISTp has a subdued, calm presence. "Stoic" is an appropriate description of the ISTp--it's hard to get them riled up, especially for someone who does not know them very well (more on this in point #3).
- The ISTp is grounded and practical. In conversation and in the way they handle various situations, the ISTp takes a practical approach (not super-logical, but just practical). They can handle adversity quite well due to their rational way of dealing with things.
- The ISTp is aloof, but friendly. While they are usually quite friendly and easy to engage, they do not take initiative, socially. They are more likely to approach someone for some practical reason (has a question or sees that someone needs assistance). They also generally maintain emotional distance in their relationships, preferring physical or practical communication over obvious displays of emotional intimacy.
- The ISTp has a thing for domestic animals. They usually will have a cat or a dog (or multiples of either/both) and seem to bond much more quickly with animals than with people. Certainly, most people love puppies and kittens, but the ISTp interacts with their pets as if they were siblings.
- The ISTp has slightly offbeat views. While they often give the impression of being conservative and for all purposes, "normal," (probably a side effect of their overwhelming calmness) the ISTp usually has a bit of an eccentric perspective on life that is revealed after some time--e.g. a bizarre hobby, a radically liberal opinion, etc.
- The ISTp [generally] has a stockier build and [usually] has a rounded face. This is true of males and females. They tend to dress well, but conservatively.