It's called the Design District for a reason: large furniture stores don't usually make for beautiful architecture. It felt pretty safe to me on several visits, and definitely up-and-coming a few years ago.
If you ignore the homeless problem (which is actually in busy areas like Tenderloin), there are no real "sketchy" areas in SF. You have to cross the bay for that.
Maybe my parameters are skewed. IMHO sketchy areas in London, Paris, Milan are more threatening than anything I've seen in SF peninsula, despite the obvious difference in guns per capita.
Can't speak to Milan but I've never felt unsafe in Paris, and only once felt unsafe in London (and that was at 3AM and I was dressed... interestingly), whereas in the space of a week in SF I had two scary encounters with ranting homeless guys.
They actually pushed many of the homeless away from Market St. to just west of the Zynga building on Division street under the Central Freeway. It is indeed pretty sketchy - tents lined up in rows, broken car windows, needles and feces on the sidewalk, people working on obviously-stolen bikes, etc.
If you ignore the homeless problem (which is actually in busy areas like Tenderloin), there are no real "sketchy" areas in SF. You have to cross the bay for that.