There's a red sign with a "U" on Union Jacks. I've heard it's a warning that the building is unsafe to enter if it's on fire. How do they stay open if they're unsafe? I love UJs, but I don't want to burn there!

—Bill M.

You may call me a pettifogging old schoolmarm, Bill, but it's my considered opinion that all buildings are unsafe to enter if they're on fire. I'm afraid I must stand firm on this: If a building is on fire—even one without a red U—it should not be considered a convivial spot to spend an evening, say, rebottling your collection of vintage paint thinners.

Of course, this rule doesn't apply to firefighters. They hang out in burning buildings all the time—often splashing a little gasoline under their arms before they walk in, just to add to the overall badassery of the effect. 

Still, there are a few buildings that, while no more likely to catch fire than any other building, present first responders with special challenges if they do happen to catch on fire. The scarlet U is a warning that, even for firefighters, this particular burning building might not be the greatest spot to hold the company potluck.

Concerns might include upper floors more-than-usually prone to collapse, or a deficiency of exits from some rooms. The Fire Bureau maintains a building-by-building database of such hazards, and the red U on a specific building reminds firefighters to check this catalog before charging in.

The Fire Bureau says these buildings are perfectly safe in their normal, not-on-fire state; they'd be shut down if they weren't. Still, if you smell smoke in Union Jacks, it might behoove you not to stay through the next dance—even if you did already put down your dollar, you cheapskate.