The phrase "bat signal" refers to a distress signal, usually displayed in the shape of a bat in popular culture, that is used to call for help or assistance from a superhero named Batman. Full definition
In addition, this particular nullification has a little extra weight, since North Korea cut off its emergency direct phone line to South Korea — a sort of bat signal one could use to call the other and sort things out when tensions got unbearable... (relevantmagazine.com)
Given there are several hundred species of bat - pollinated flower in Central and South America, and 40 bat species highly adapted as nectar feeders, Simon's team expects to find more strangely shaped bat signals on plants. (newscientist.com)
Taking it to be a Biennale bat signal of some sort, I walked in to find a white - maned gentleman sitting and smoking at the far end, with his phone plugged into a portable charger. (artnews.com)