It is worth pointing out that No. 134's indication for the people to make the triple sign of the cross is a novelty of the third edition of the Roman Missal. It was not found in the corresponding No. 95 of the earlier GIRM from the 1970s, where the gesture was prescribed only for the minister reading the Gospel. In making this indication the missal simply recognizes a practice which had already become almost universal among the faithful over the centuries.I had wondered about that when the new edition came out, (though not enough to look into it,) and apparently my memory of all that was correct.
(This is timely for me, because I was thinking of devising "Simon Peter Says, a game of liturgical gestures to play when we need to blow off some energy when things get too rambunctious in RelEd.)