On the America blog, James Martin, S.J., raises the issue whether Pope Francis remains a Jesuit. His conclusion is:

So yes, traditionally, the Pope is still considered a Jesuit.

Perhaps "traditionally" could be parsed: "in his heart of hearts."However, there is an interesting comment to the post which might be deemed a "fraternal correction." Jim McDermott, S.J. suggests:

When the Pope was first made a bishop, he was released from his Jesuit vows of poverty and obedience to his religious superior. At this point, canonically he left the Society....To say he was no longer a Jesuit canonically is not to say Jesuits shunned him or even thought of him as anything less than a brother, or that he thought of himself as no longer a Jesuit. As you point out, he signs his name with an S.J. The General likewise has referred to him in this way.But all of that is a matter of respect and as you say tradition, not law. No longer obedient to the General, he is not canonically a Jesuit.

The first Jim seems to concede the second Jim's point when he writes:

Yes, the Superior General of the Society of Jesus is obedient to Pope Francis, not the other way around.

Speaking neither as a canonist nor a member of a religious order, I would prefer that when members of religious orders accepted episcopal ordination and responsibility, they would no longer use the identifying initials of their former religious communities after their names. If the Bishop of Rome will no longer put "S.J." after his name (or "O.P." or "O.F.M."), neither should other bishops.