call
嚆 centers on calling out or shouting, often in a loud or urgent way.
嚆 combines 口 (mouth) with 蒿, which likely contributes the sound. The exact historical development of 蒿 in this character is uncertain.
The mouth 口 on the left is paired with 蒿, which looks like a tall plant with a high top. Imagine someone calling out from the top of a tall stalk, their voice carrying far.
For コウ, picture a person calling out "Kou!" from the top of the tall 蒿 structure: the sound "Kou" cues コウ while the mouth 口 calls.
whistling arrow used to signal the start of battle