You're the author, choose the wording, up to 20 letters,  across the arms.  Here are some examples.

Caution..Out of Service

Danger..Danger..Danger

Sorry..Not in Service

Closed for Repair

Closed for Cleaning

This area Closed

Stay Away..Stay Clear

Danger..Keep Out

Fresh Wax..Wet & Slippery

Caution..Wet Floor

Restroom Closed

Caution..Work Area

Area Closed..Keep Out

Caution..Construction

Caution..Do Not Enter

Caution..Men Working

Caution..Women Working

Caution..Watch Your Step

Danger..Chlorine Hazard

Closed for the Night

Danger..Hard Hat Required

Danger..High Voltage

Danger..Men Working Above

Elevator Closed

Escalator Closed

Hazardous Area

Pardon Our Dust

Please..Quite Zone

"The Boys" are currently working hard at...

Digital Equipment Co.

Polk General Hospital

Naval Supply Center

Westinghouse Electric Corp.

Blue Cross/Blue Shield

U.S. Postal Service

Pennsylvania State University

Litton Electronics

Indiana Power & Light

U.s. Army Corps of Engineers

Standard Oil Building

The Hearst Corp.

Rockefeller Center

Empire State Building

Honeywell, Inc.

3M Company

Memorial Hospital

Tri-City Airport

Albuquerque Int'l Airport

Days Inn of America, Inc.

Government Services Admin.

AT&T Teletype

Xerox Corp.

General Motors Corp.

Sears Tower

Alabama Power Company

Hartford Hospital

JF Kennedy Int'l Airport

and the list goes on an on......