HP 81101A Reference Manual page 9

Capacitors inside the instrument may retain a charge even if the
instrument is disconnected from its source of supply.
Safety Symbols
Instruction Manual symbol: The instrument is marked with this symbol
when it is necessary for you to refer to the instruction manual in order to
protect against damage to the instrument.
Protected conductor symbol.
In the manuals:
WA RN IN G
Warnings call attention to a procedure, practice, or the like,
which, if not correctly performed or adhered to, could result in
personal injury or loss of life. Do not proceed beyond a Warning
until the indicated conditions are fully understood and met.
C A U T I O N
Cautions call attention to a procedure, practice, or the like, which, if not
correctly performed or adhered to, could result in damage to or
destruction of part or all of the equipment. Do not proceed beyond a
Caution until the indicated conditions are fully understood and met.
Safety Information
9