Aharon,
If they’re just numbered sequentially, this expression for source text will give the number of the most recent marker:
L = thisComp.layer(“audio layer”);
n = 0;
if (L.marker.numKeys > 0){
n = L.marker.nearestKey(time).index;
if (L.marker.key(n).time > time){
n–;
}
}
if (n==0)”” else n
Dan