When notating a single move by black, or a sequence of moves that starts with a move by black, an ellipsis is generally used. There is no one universally accepted convention as to its appearance though. For instance, one might write
2. ... Nc6 or instead prefer
2... Nc6. Both are in use: an instance of the former at wikibooks, an instance of the latter at wikipedia. I happen to prefer the former, but the purpose of this post is to propose:
Either convention is perfectly acceptable, and we need not seek uniformity across all posts in this regard.
If a poster prefers one over the other, I think there is no reason to change it in either direction. Thoughts?
(What brought this topic to mind is that my recent question was edited to switch from the first convention to the second, and I decided to roll back that edit, because I prefer the way the first convention looks.)