No, the plug comes with a smooth face. It is fitted with the hooked breech tang in a earlier part of the build, the very first step in my case. Toward the end, the vent is located and drilled. The drill marks the plug threads. Go slowly here, you defiantly do not want to have the bit jam and break off. The plug is removed. The notch is then filed with a round file down to the mark from the vent drill. I did not make a V-notch, as with a triangular file. I polished the notch to eliminate all file marks. The plug is then reinstalled. The plug is timed to the flat on the barrel for the lock fence. The tang has a corresponding flat that was previously filed, or milled, to match perfectly. I check for alignment by running my finger nail over the seam and index the plug to make it perfect again.
I never use index marks to line up plugs. I use the method I described above. I do the same with the top flat of an octagon barrel. Once you file them to be one, you have a perfect index reference.