The phrase Spes In Deo ("Hope In God"), as well as its variant In Deo Spes are popular inscriptions found on ecclesiastical rings. Here I have a visualization of a modern gold ring design featuring these words.
Other well-known religious ring inscriptions include:
Deus dona vivas in Deo – May God grant that you may live in God
Vivas in Deo – May you live in God
In Hoc Signo Vinces – In this sign thou shalt win
Laus Deo – Glory be to God
Mater Dei Memento – Mother of God, remember (me).
Prayers and excepts of prayers can also be engraved on rings. Some historical examples of such engravings are:
AVE MARIA GRATIA
MARIA, ANNA, IH’US
Sometimes the prayers are not engraved, but rather represented by small knobs that can be used as beads for repeating Ave . Eleven knobs would signify eleven Aves and one Pater Noster . Such rings were called "decade rings", the term which was occasionally used in a corrupted form of "dicket rings".
The Greek letters Alpha and Omega are also often used in Christian ring designs, as well as Chi and Rho.