Editor shows yellow triangles when Clang code model is active

When the Clang code model plugin is active, the text editor shows yellow triangles to the left of the line numbers, on some lines.

There must be a reason why they're shown, but it's not apparent. If there's a way to get more information from them, it's not evident or discoverable. I tried clicking on them, but that simply sets a breakpoint. I tried right-clicking it and it shows options that don't differ from every other line (breakpoint, message tracepoint, bookmark).

Update

There should be a red underline somewhere on that line, but it doesn't show. That's a problem with the font.

Even after switching to a font that shows the underline, hovering over the marked symbol still shows no information.

This would be very useful if the warnings are all shown in the Issues panel so It can be found
at one place without opening each file in turn?