We dont see this citation very often, but it is a standard and it is one that we use often…
1910.144(a)(1)(iii) Stop. Emergency stop bars on hazardous machines such as rubber mills, wire blocks, flat work ironers, etc., shall be red. Stop buttons or electrical switches which letters or other markings appear, used for emergency stopping of machinery shall be red.
Here is an OSHA citation from this week: