From usage it looks like it's an isolator or a transistor, but I can't find what exactly it means on any chart of component symbols. This is a DMX sheild. Its interesting that two of them are being used with both outputs, apparently to go to two different voltage levels? One says arduino TX and RX and the other says VTX and VRX. But the pair on the left don't split, they go to an enable and one ties to ground while the other ties to vcc. These are probably really common protection circuits but I'm not sure what to look up to check them. I figure I could learn from reading about it.