S's tend to use and apply what otherís have done. I know some very smart S's. They all work hard at learning their stuff, even the ISTP I know. They tend not to be very imaginative. And at least from my limited observation, tend not to care so much why something works only that it does. You might get an S who is a brilliant mathematician. Such a person might learn various theorems and mathematical techniques inside out in terms of how to apply and interpret them, but they might not care so much why these things work. I want to know "the why" behind everything. Makes learning a very slow process. I like N's because we are on the same wavelength, most of the time.
So you could potentially detect an S because they demonstrate a pattern of not caring about the meaning behind things. Sometimes they might miss what seem like obvious connections.