25 Pa. Code § 227a.12 – Labeling.

(a) General rule. A radiation-producing device must be labeled with a readily visible and discernible sign or signs bearing the radiation symbol and the words: ‘‘CAUTION RADIATION—THIS EQUIPMENT PRODUCES RADIATION WHEN ENERGIZED,’’ or words having a similar intent, near every switch that energizes an X-ray tube.
(b) Devices with designed openings. For radiation-producing devices with designed openings for object entries, such as baggage units, the following must be posted at or near every opening: ‘‘CAUTION—X-RAY HAZARD: DO NOT INSERT ANY PART OF THE BODY WHEN SYSTEM IS ENERGIZED’’ or words having similar intent.

This section cited in 25 Pa. Code § 227a.3 (relating to exemptions).