Retroreflective sheeting or other approved retroreflective materials must be used on all signs that do not have sign illumination, unless the sign standard as included in the Pennsylvania Handbook of Approved Signs (Department Publication 236M) indicates that the sign does not need to be retroreflective. Type III or higher type retroreflective sheeting is encouraged to improve nighttime visibility of signs, especially for older drivers.
67 Pa. Code § 212.104