Does anyone know what third-party app uses this menubar icon?

This icon appeared on the right side of my menu bar; it had no name or dropdown menu when I moused over it or selected it. ![macOS menu bar icon consisting of a vertical line with diagonal line running NW to SE and down arrow in SE corner] I researched Apple documentation and believe it's something I installed and not part of the OS. Does anyone recognize this or know how to sort out which app injects an icon into the menu bar?