The surfaces on a Special Mint Strike should (usually) be smoother because more care was taken preparing the planchets. If they have fewer dings and marks before being struck, the finished coin will, too. In your picture you can see that the bottom middle of the steps are missing. The top picture (below) shows how the better strike forces the metal fully up into the die, giving sharp steps with lines all the way across. Compare the surfaces of the two coins. The SMS is generally smooth in the fields and fully detailed everywhere. The business strike is just rougher all over, since it was struck on a planchet that was stamped out without much care, then tumbled in a dryer with many other planchets. These rough marks survive the minting process and can be seen all over the coin - especially behind Lincoln's head, on his shoulder, and in the fields under the Lincoln Memorial. Here is a 1965 SMS (Special Mint Strike) and a 1965 business strike, also from the Philadelphia mint.
I saw this right after he posted it. But I didn't know what an "rs" penny was either so I moved on. Goes back to the posters know in their head their question(s) but don't spend the few seconds extra to be as clear as possible.
