Incest indicators?

[~Elizabeth~]

Maybe if a woman has a son, and her son's ydna matches her male relatives. Maybe if a man's ydna exactly matches a male relative on his mothers side.

I used to know someone who was raised by his grandfather. He eventually found out that his grandfather was also his biological father. And he found out that his big sister was also his mother. That was in 1996 and not by dna testing.

Is there anything in a DNA test that offers any indication of possible incest in the ancestry? For example, if your 2X great grandfather and 1X great grandfather were the same person, or if a great uncle and great aunt were siblings. I assume there would be nothing definitive in testing a single person, but I wonder if there might be some suspicious clues.