triangle "flags" at start and end

I was editing and suddenly they appeared around the measure that was currently selected. When I tried to undo, all it did was remove the last actual notation edit I had done. Once I clicked out of the measure, the flags moved to the start and end of the score. They also appear on other scores I have open (or when I open another) so must be some sort of setting I accidentally toggled? I have no idea what they are for, what I did to make them appear, and most importantly, how do I get rid of them?