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I am extremely skeptical of this claim, but I think it would be worthwhile for someone to post a debunking of this claim if possible, rather than simply downvoting it. Most anachronistic "alternative history" artifacts seem to be easily debunked with a quick Google search.

My own search on this one yielded no results but did indicate that other runic stones in the NE United States are considered to be hoaxes. Perhaps we can assume the same here. But again, some further commentary would be valued.

I think /u/wee_little_puppetman or another viking focused mod would be the best to answer.

See this thread http://www.reddit.com/r/AskHistorians/comments/1vrill/do_we_know_now_that_vikings_landed_in_america/

Where in PA is this?

Indiana PA

Also if you were 20 feet away, you would never see the petroglyph.