Here's what I found after some digging.
Facts: I've got OEM Toyota glass in my 2010 Limited, with the heating element (how it's survived this long I can't answer). Here are some pics. You will notice, no A-S1 line, no factory tinted strip either, but it does have an A-S1 marking in the same spot as OP's.
Without getting into specifics, the A-S1 marking pretty much shows that the glass meets certain quality standards (here we're interested in "luminous transmittance"). The Federal Motor Vehicle Safety Standards (see: FMVSS 205) requires windshields to comply with ANSI Z26.1 - which is where our A-S1 designation comes from. When you see an A-S1 line on the windshield, the manufacturer is pretty much saying that from this line down (which ever way the arrow points actually), the glass is intended to comply with A-S1 standards. In our case, the
entire windshield is certified as A-S1. So if your code requires nothing below the A-S1 line, then no tint for you. Most states fall back on the FMVSS 205 as their baseline for tint.
Opinions: You live in PA. Read your laws as they apply to you and only the members on this forum who garage their trucks in PA. A quick search revealed that your state's statutes do not specify percentages, but your state's code does. See section 175.263 specifically. Here you'll notice that FMVSS 205 pops up again. Essentially, you cannot tint your windshield in a way that doesn't allow a minimum of 70% light transmittance. Since you don't have an A-S1 line, and there is no factory tint along the top, you probably wouldn't be able to argue any windshield tint in court (not a lawyer, which is why this is in the opinion section). You can however apply for a medical exception per PennDOT. That said, a few of my police friends here in VA don't pull over for tint strips but they clean house on full windshield and front side window tints in general (but our code is much more strict).
OA
Sources here as I was too lazy to cite in my explanation:
https://www.federalregister.gov/articles/2012/06/21/2012-14996/federal-motor-vehicle-safety-standards-glazing-materials
(On your own for ANSI Z28 - work pays for that but I can't access it from home)
Pennsylvania Code
Title 75 - PA General Assembly
http://www.dmv.state.pa.us/pdotforms/fact_sheets/fs-sun.pdf