"Can I take a glance at your code?" - If applying for an programming position, this is one of the leading indicators of how well the team works regarding refactoring, communication, and their philosophy towards coding.
I took to asking to see samples of real production code at all my interviews towards the end of my time working as an employee.
No-one ever objected. In fact, most places seemed glad I was interested and thought it was a reasonable request. It was pretty common to be asked to wait until the second interview, though, as most places wouldn't be kitted up to do this without notice.
The chances of you seeing a section of code that is central to their IP and the answer to the question, "how did they do it?" and, additionally, your ability to instantly understand it are very slim.
This is a great question for an engineer to ask. Being able to see if the code is smart (e.g. using shorthand instead of multiline logic), neat and documented is a great way to get a feel for how your potential future coworkers work. They've spent the last two to four hours grilling you and know you, how you code and how you solve problems pretty intimately -- why not get to know them better, too?
Don't you ever watch movies about programmers? That's exactly how it works. The protagonist looks briefly at some code before declaring "Oh wow, this guy is good." For added realism, he should be typing the entire time.
You don't ask to see the code so you can identify the really good places, you ask so you can run away from the really bad places. It's the flip side of employers asking for basic coding tests: it's not there to tell you how good the good guy is, it's there to get rid of the guy with the great-looking CV who can't write "Hello, world".
At one of my round 2 interviews (for an internship, so entry-level stuff), a large part of the interview was them showing some of their code and quizzing me on what it did and so forth.