36 Pa. Stat. § 2720.2
The following words and phrases when used in this act shall have the meanings given to them in this section unless the context clearly indicates otherwise:
"Department." The Department of Transportation.
"Obstruction of view." When the intent of the advertising is not discernible for a total of five seconds in the viewing zone.
"Off-premises outdoor advertising device." An outdoor advertising device as defined by, and for which a permit has been issued pursuant to, the act of December 15, 1971 (P.L.596, No. 160), known as the Outdoor Advertising Control Act of 1971, or for which a permit has been issued pursuant to any local ordinance and which advertises activities not conducted on the property on which it is located.
"On-premises outdoor advertising device." An outdoor advertising device which advertises activities conducted on the property on which it is located.
"Outdoor advertising device" or "device." Both on-premises outdoor advertising devices and off-premises outdoor advertising devices.
"Screening" or "screened." The obstruction of view of a device as viewed from the center of the lane of traffic of the highway and from a height of no more than 60 inches above the highway surface.
"Vegetation." All woody and herbaceous plants growing within the legal right-of-way as described in section 410 of the act of June 1, 1945 (P.L.1242, No. 428), known as the State Highway Law.
"Viewing zone." That distance measured along the center of the lane of traffic of a highway which a vehicle will travel at the posted speed limit.
36 P.S. § 2720.2