PA
(d) Obstructions. A vehicle specified under this subchapter shall have glazing free from obstructions as described in 175.80 (relating to inspection procedure).
(1) With the exception of materials in paragraph (4), signs, posters or other materials whose design prevents a driver from seeing through the material may not be placed on the windshield, a side wing, a side window or rear window so as to obstruct, obscure or impair the drivers clear view of the highway or an intersecting highway. Under FMVSS No. 205, these restrictions do not apply to the rear side windows, rear wings or rear window of trucks or multipurpose passenger vehicles.
(2) With the exception of materials in paragraph (4), signs, posters or other materials whose design prevents a driver from seeing through the material may not be placed on a rear side window, rear wing or rear window of a passenger car which either covers more than 20% of the exposed portion of the windows or wings, or extends more than 3 1/2 inches above the lowest exposed portion of the windows or wings.
(3) This subsection also applies to glass etchings, except those used for vehicle identification.
(4) A sun screening device or other material which does not permit a person to see or view the inside of the vehicle is prohibited, unless otherwise permitted by FMVSS No. 205, or a certificate of exemption has been issued in compliance with 175.265 (relating to exemption provisions). See Table X for specific requirements for vehicles subject to this subchapter. Passenger car requirements relating to the rear window are delineated by vehicle model year in Table X.
(5) Vehicles specified under this subchapter may not have an obstruction forward of the windshield which extends more than 2 inches upward into the horizontally projected vision area of the windshield with the exception of windshield wiper components.
That is PA's law. Basically as long as you can see through it, its legal. My friend has 15% and was pulled over for it and they let him off. The only seem to hate 5% (limo). As long as your car has passed inspection w/ the tint you can't get a ticket. They aren't allowed to pass a cars safety inspection if its too dark.