Although "reach" or "grip" are usually good translations for "greifen", those terms are normally not used for machinery hazard warnings. Expressions like:

"Danger – Hands off (components while in motion)!"

"Danger – Do not touch (components while in motion)!"

Danger – Do not place hands in/on … (components while in motion)!"

"Danger – Keep hands away from/out of … (components while in motion)!"

are often used.

HTH

Dan