67 Pa. Code § 212.404 – Sign supports.

(a) Post-mounted signs. Post-mounted signs or signs on fixed supports shall be installed in accordance with the Signing and Marking Standards (Department Publication 111M).
1. (1) Post-mounted sign installations must be of a breakaway or yielding design unless they are adequately placed behind guide rail or median barrier.
2. (2) Signs may not be mounted on existing utility poles or other structures unless the owner grants written permission and the signs can be properly positioned to convey their messages effectively.
(b) Portable sign supports. Portable sign supports must be of a type approved by the Department and listed in Approved Construction Materials (Department Publication 35).