Hi,
There is probably no symbol for high current because you dont get high current unless you try or you make a mistake. And anyone that designed a circuit that had high current would have already figured out how to handle it. But yes, there could be a potential for high current which maybe the operator doesnt realize, such as with a 10,000 watt 10v power supply <chuckle>. In this case accidentally shorting it out could mean a disaster. Just like a 12v automobile battery, it would be perhaps a good idea to put some sort of high current warning on them because if accidentally shorted out it could blow up and injure the user. So a high current warning on some things sounds like a good idea to me.