Acoustic Research WHT24 Manual De La Instalación Y De La Operación página 5

WHT24
The lightning flash with arrowhead symbol within an equilateral
triangle is intended to alert the user to the presence of "dangerous
voltage" within the product's enclosure that may be of significant
magnitude to constitute a risk of electrical shock to persons.
The exclamation point within an equilateral triangle is intended to
alert the user to the presence of important operating and maintenance
(servicing) instructions in the literature accompanying this product.
page 3