[mrexroad]

Interesting! Per your Wikipedia link… there was an early ‘00s proposal for a dedicated sleep symbol: line through a crescent moon. Same proposal would have defined line-through-circle as the generic power symbol. Though, this was superseded with standard for using only a crescent moon to indicate standby.

“Standby symbol ambiguity

Because the exact meaning of the standby symbol on a given device may be unclear until the control is tried, it has been proposed that a separate sleep symbol, a crescent moon, instead be used to indicate a low power state. Proponents include the California Energy Commission and the Institute of Electrical and Electronics Engineers. Under this proposal, the older standby symbol would be redefined as a generic "power" indication, in cases where the difference between it and the other power symbols would not present a safety concern. This alternative symbolism was published as IEEE standard 1621 on December 8, 2004.”

Edit: formatting, verbosity.

[contingencies]

there was an early ‘00s proposal for a dedicated sleep symbol: line through a crescent moon

This may have been avoided owing to strong potential of religious misinterpretation.