Used by climbers and lifters, even acrobats at height. Or snapped with a string that's pulled very tight. I can write in many colors, the most common is white.

I don't eat light, yet I burn fat. Forget me not, or I will attack.

I sense that smells for without me you surely will fail

If acoustics allows for me, you'll swear that it's you, times three.

Despite its name, ladies can also deliver letters here