when rightside up, the “A” with extended crossbar means , but when upside down, the closest glyph is an .
UPDATE 09.02.25: i just learned that the upside-down capital “A” is a mathematical symbol meaning “for all” (and can be written in html with the string & # 8 7 0 4 ; with no spaces). so the sign reads CH for all OS CONTROL. maybe OS means “operating system”? so “for all operating systems: control”? what “CH” refers to remains a mystery.