Laws regarding rear-view windows

What is the name of your state? Pennsylvania

Great site, hopefully you won't think my idea is stupid I would like to mount a scrolling L.E.D. sign in the rear window of my vehicle ( at the bottom corner of the driver's side rear window...) The L.E.D. sign is 4"X20" and has red L.E.D.s. I want to use the sign as basically an "electronic bumper sticker" that would scroll messages of my choice. Alternately, it could tell tailgaters to "BACK OFF", etc.

Is this application legal in PA (would I get a ticket?) If yes, what laws / sections would I be breaking? The 2 possible issues I see are "distractions" and "obstructing the rear window" -- but can't seem to find the exact laws that apply. Thanks in advance for any help !

[JETX]

In most states (that use red emergency lights), exhibited scrolling or moving red lights in your back window would be illegal.

Thanks for your quick reply, Halket!

Do you know where I could (easily without spending months poring over legal manuals in the local library) find the exact laws that surround this issue?

I guess what I'm asking is : are the only issues with using such a sign the fact that the L.E.D.'s are red? If the sign displayed a different color, say, green or blue or yellow or purple -- would it be legal then?

Mabie the real question is what conditions would have to be met in order for me to legally do an "electronic bumper sticker" thngy ?

Any information you can provide would be great. Thanks !