Have you seen this symbol before? Probably not and for good reason. It’s new and it’s important. This is the new symbol adopted by the International Organization for Standardization’s (ISO) to denote a potential danger from arc flash.
It will doubtlessly take a while to roll out and start showing up on electrical boxes and generators but if and when you do see it either stay clear or, if you do need to work on the panel, make sure you are wearing the appropriate PPE designed for that level of potential arc flash.