Today we observe the Solemnity of St. Peter and St. Paul. The Norms of the Church say this:
|St. Paul and St. Peter, by El Greco|
N.17. The faithful who use with devotion an "object of piety" (crucifix, cross, rosary, scapular or medal) properly blessed by any priest, can acquire a partial indulgence. But if this "object of piety" is blessed by the Supreme Pontiff or any bishop, the faithful who use it devoutly can also acquire a plenary indulgence on the feast of the holy Apostles Peter and Paul, provided they also make a profession of faith using any legitimate formula.
An explanation of indulgences can be found here.