Characters in the Symbol font are not showing up correctly on the plot.
There could be a problem with the font cache on the Mac. The easiest way to clear the font cache is to reboot into Safe Mode by holding the Shift key immediately after a restart. A progress bar should appear, during which time the system will run various checks behind the scene, which includes clearing the font cache. After the system boots up, you could launch KG to see if things are working and then restart normally to get out of Safe Mode.