NEC 2300 DL - Manual (Page 164)

Safety Information 156
Warning and Precaution Symbols
Meaning of Symbols
Ignoring this warning could cause serious injury or
even death.
Ignoring this caution could cause injury or damage to
property.
A triangle indicates a danger against which you should take precaution.
This symbol warns against burns.
A diagonal line indicates a prohibited course of action.
This symbol warns against dismantling the device.
A black circle indicates an imperative course of action.
This symbol indicates you must unplug the device.
or
WARNING! !
or
Attention