I know some folks are probably tired of hearing me say this, but
this is why I keep a whistle in my teeth. There are times that a
motorist must be reminded of my presence, especially when
they "can't see me."

It's not just a theory. I have used my whistle many times to "wake up" a driver, possibly preventing a collision (with me.)
It just pays to have more than one way of attracting attention to yourself.