I guess the idea here is that the G, L, B or T person, or any combination thereof, will see the sign and no longer have to shout out: "PLEASE, FOR THE LOVE OF GOD! DON'T PUMMEL ME!" as they approach you in your cubicle. That kind of stuff is very disruptive in cubicle land.
I've worked in the corporate world for a long time. I've never heard people bring up GLBT stuff in conversation. Well, actually, there was one person who would bring it up, and he was gay. And he'd introduce the topic out of the blue with comments such as "(Sigh)....sometimes I think all I want out of life is to find a nice man to settle down with." And I'd say something like, "Well, that's just swell, Mike," and change the subject. That's just my Midwestern sense of propriety, you know.
I have worked with many gay people throughout my employed life. During working hours it was never a topic of conversation, they never brought up or used their 'sexuality' in anyway. Private conversations during lunch or drinks after work, sure. But never in the work place.