I read something that said the circles were the sun, earth and moon. Heathbaby.com?
http://www.vanishingtattoo.com/tattoo/celeb-ledger.htm
Center of the Universe tattoo designed by Heath
those are good pictures of some of his older tatoos in that link thanks for posting it.
Yes that circle with the black/white opposites on his shoulder does represent a yin/yang thing I think.
and the three circles on his other shoulder--I had heard they are Australian aboriginal tribal designs, -could well be sun/earth/moon as you said---and sometimes depending on the movie they get turned into a Celtic cross--depending on the Director's vision---it is all makeup but something to know anyway. I don't believe that ROAR tat around his bicept is permanent though, I just think that was for the series, it certainly isn't showing up now when he is in a tank top.
I was referring to the big black rectangle with the 3 smaller circles in it on his forarm--as representing the Ledger family-as he had both Michelle and Matilda in the tattoo parlor when he had it done. But he hasn't really said anything about what they are to him as of yet. But it also could represent as you said the S/E/M.
My favorites still though are KAOS on wrist, Old Man River on lower forarm, and his leaf tat on his hand. Just really like them and all they represent to him and me. LOL