A double "Alleluia”, added at the end of the “Benedicámus Domino” and again after the response “Deo grátias” and that is that until the great night of the vigil.
Over at New Liturgical Movement, there is an interesting article that details how the Fraternity of St Joseph the Guardian in La Londe-les-Maures, France actually bury the Alleluia.
Of course, the changes brought in with the Novus Ordo buried the season of Septuagesima.
For those not familiar with the Old Rite or are not old enough to remember the lovely pre-Lenten season of Septuagesima, I would recommend that you watch this short video made by the LMS and which gives some insight into this not so lost season.