Today, I have read the prænotanda to several blessings in the Roman Ritual: Book of Blessings and the answer to the OP’s original question (“can lay persons bless things?”) is yes. What I find less clear is whether the words may be accompanied by any gestures, such as outstretching one’s hand towards the person or object to be blessed, or signs, such as making the sign of the cross over the person or object, or if the layperson should keep their hands joined.
One has to distinguish between “official rites of blessings” according to the rites in the Book of Blessing or other like things (LOH) and those which are just Lay persons praying and blessing…like parents blessing their Children.
For the first…there are clear rubrics. A Lay person in those rites does not do the same thing Priests or Deacons do …like make the sign of the cross over things etc (they make it on themselves)…and the words are different. Theologically of course the blessing here is different too! As noted above.
Also it is to be noted that a Family can use this rite to bless their house…but there is NO blessing for them to for say blessing a rosary or medal.
Both the Priests and Deacons and the Lay persons here are using the official rites (some only can be used by Lay persons).
On the other hand any Christian is called to “bless” in various ways…
vatican.va/archive/catechism/p2s2c4a1.htm via prayer…the sign of the cross…even use of holy water … These are simply Christian living…not official rites. There is no prohibition of making the sign of the Cross over things as far as I know (outside the formal rituals) (and again they can not bless Crucifixes or medals etc) …as did the early Christians. But again their blessing is very different than that of the Ordained. But I think it is good to avoid confusion…to not do it “like an ordained priest”.
“every baptized person is called to be a “blessing,” and to bless.” (CCC1669)
The sign of the cross has been used since the very early days… Early Christians would use it all the time…
in the early Church it was made on the fore head with a + (and still is at the Gospel…and one can of course always use do it this way too personally outside formal liturgical times…i do…) But also over things…like their meal etc it seems.
“let us then not be ashamed to confess the Crucified. Be the cross our seal, made with boldness by our fingers on our brow and in every thing; over the bread we eat and the cups we drink, in our comings and in goings; before our sleep, when we lie down and when we awake; when we are travelling, and when we are at rest”.
St. Cyril of Jerusalem (300’s AD)
In all our travels and movements, in all our coming in and going out, in putting on our shoes, at the bath, at the table, in lighting our candles, in lying down, in sitting down, whatever employment occupies us, we mark our forehead with the sign of the cross."
–Tertullian (c. 160 – c. 220 AD)
“Making the sign of the cross – as we will do during the blessing – means saying a visible and public “yes” to the One who died and rose for us, to God who in the humility and weakness of His love is the Almightly, stronger than all the power and intelligence of the world.”
-Pope Benedict XVI
Angelus
September 11, 2005
he also talks about it when he was Cardinal in the Spirit of the Liturgy…where recalls the blessing with the sign of the cross on his forehead by his parents… desiring such to be more practiced today…
But YES it is very important to distinguish between the blessing of a Priest etc and that of a Lay person. The Sacrament of Holy Orders and his vocation in the Church …and the intercession of the Church make it something very different. (Which is a great gift for us!)
And that of a Bishop…particularly the Pope is even more so!