As an example to highlight my point, I used the gesture of making the Sign of the Cross on one's forehead, lips, and on one's breast just before the Gospel reading is proclaimed during Mass. In my zeal to make my point, I wrote, "this custom is nowhere called for in the rubrics and is not, at least to my knowledge, a universal practice. It is widespread, it seems, throughout the United States."
As it turns out, I was mistaken. After looking into the matter a bit more, specifically at the General Instruction of the Roman Missal, or, in shorthand, the GIRM (pronounced "germ"), I (re-?)discovered this called for gesture. In the instructions for "Mass without a Deacon," it is stipulated (par. 134)-
At the ambo, the Priest opens the book and, with hands joined, says, The Lord be with you, to which the people reply, And with your spirit. Then he says, A reading from the holy Gospel, [according to St. Matthew, Mark, Luke, John,] making the Sign of the Cross with his thumb on the book and on his forehead, mouth, and breast, which everyone else does as well. The people acclaim, Glory to you, O Lord. The Priest incenses the book, if incense is being used (cf. nos. 276-277). Then he proclaims the Gospel and at the end pronounces the acclamation The Gospel of the Lord, to which all reply, Praise to you, Lord Jesus Christ. The Priest kisses the book, saying quietly the formula Per evangelica dicta [, deleantur nostra delicta] (Through the words of the Gospel [, may our sins be wiped away])- all italicizing, emboldening, as well the added words in brackets (added from the Roman Missal) are mine
In the instructions for "Mass with a Deacon" (par. 175) read:
At the ambo the Deacon greets the people, with hands joined, saying, The Lord be with you. After this, at the words A reading from the holy Gospel, [according to St. Matthew, Mark, Luke, John,] he signs with his thumb the book and then himself on his forehead, mouth, and breast. He incenses the book and proclaims the Gospel reading. When this is done, he acclaims, The Gospel of the Lord, and all reply, Praise to you, Lord Jesus Christ. He then venerates the book with a kiss, saying quietly the formula Per evangelica dicta [, deleantur nostra delicta] (Through the words of the Gospel [, may our sins be wiped away])- all italicizing, emboldening, as well the added words in brackets (added from the Roman Missal) are mineThis correction came was prompted by reading the answer to a question posed to Padre Antonio over on Aleteia. He writes nicely about what this Tradition, this custom, this gesture means: "We are all invited to examine ourselves on how we receive the Gospel, how we involve ourselves in the proclamation of this message, and how we conform our lives to its instructions. We are called to become an 'illustrated Gospel' – the 'fifth Gospel,' written not with ink but with our lives. We receive with the mind, we proclaim with our lips, and we preserve the treasure of the Word in our hearts. Along this road, let us entrust ourselves to the Lord to be a reflection of the true light through the darkness of today’s world."
Fortunately, my mistake does not undermine the point I sought to reinforce, but arguably makes it stronger.