I found this fascinating, and you might too if you are interested in such things. It comes from the May 13 edition of Zenit, in Fr Edward McNamara’s liturgy column:
Q: I noticed that the Holy Father is carrying a new processional cross. Can you tell us about that new cross and perhaps why the Holy Father made the decision to carry this new cross rather than the one that he has carried for the past several years — the same one that Pope John Paul II carried? Are there norms and guidelines for what type of shepherd’s staff the Holy Father can carry? — B.D., Columbia City, Indiana
A: I too have noticed this new pastoral cross used by Benedict XVI. While I have no particular insights into the Holy Father’s mind, I doubt that we need to try to dig out profound theological motives. The most probable reason is that he found this cross more to his taste than the other one.
The slightly abstract pastoral staff that John Paul II carried all over the world was first designed for Pope Paul VI, a connoisseur and promoter of modern sacred art. The Italian Pope established a modern arts gallery in the Vatican Museums and commissioned the huge Risen Christ bronze sculpture in the Paul VI audience hall.
Before the conciliar reform the use of a crosier or pastoral staff was almost unknown in papal liturgies.
This was because the practice of assigning the pastoral staff to a bishop did not originate in Rome but, probably, in Spain during the seventh century from whence it spread to the rest of Europe.
The popes never adopted the use of the crosier. Even today the new rite for installing a pope foresees the imposition of the pallium and placing of the Fisherman’s Ring, but not the handing over of the pastoral staff.
Among the reasons adduced for this omission during the Middle Ages was that it would be improper since the reception of the pastoral staff implied investiture on behalf of a superior whereas the popes received their power from God alone.
On some rare occasions, however, such as the opening of the Holy Door and the consecration of a church, the popes did use a staff surmounted by a cross and this custom was adopted after the liturgical reform which foresaw a much more frequent use of the pastoral staff in papal liturgies.
The cross that Benedict XVI has been using belonged originally to Pope Blessed Pius IX and is much lighter than it looks. This is another plus, considering Benedict XVI’s age.
There is no particular law that would oblige the Holy Father to choose one design of cross over another, and it is entirely a question of pontifical artistic sensibility.