49 CFR 299.429: Rescue access windows.

(a) General. Each emergency egress window required by § 299.427 shall also serve as a means of rescue access.

(b) Ease of operability. Each rescue access window must be capable of being removed without unreasonable delay by an emergency responder using tools or implements that are commonly available to the responder in a passenger trainset emergency.

(c) Marking and instructions. (1) Each rescue access window shall be marked with retroreflective material on the exterior of each car as specified in § 299.423. A unique and easily recognizable symbol, sign, or other conspicuous marking shall also be used to identify each such window.

(2) Legible and understandable window-access instructions, including instructions for removing the window, shall be posted at or near each rescue access window as specified in § 299.423.