Well, you’ve made some guesses.
Your sugar sifting spoon was made in Paris by Pierre-Nicolas Sommé, using his second mark of a hand holding a bunch of laurel. Sommé apprenticed in 1747 to Edme-Thomas Laurent, and later transferred to Eloy Guérin. He first registered a mark on 17 July 1760. He worked at rue St-Eloi until 1793, and retired to Versailles, where he was still alive in 1806. He had a long career, and a long life.
The other marks on your spoon are: the crowned A charge mark, in use from 1774-1780, the crowned O date mark for 1777, two other marks which presumably are a discharge mark and perhaps an export mark, although they are too blurry on my monitor to read properly.
The pattern of your spoon is called Filet or Thread. It is a well executed example, with a chased-in double thread, and a reinforcement around the bowl of the spoon. The biggest collector of sugar sifting spoons, Bilgi Kenber, has published a typology of piercing styles, should you wish to pursue further. There is an engraved personalization of a marriage coat of arms under what looks like the coronet of a marquis on the spatula, although again the image is too blurred to tell with certainty.
An example of a sugar sifting spoon by Sommé is in the Puiforcat collection at the Louvre.
You have made a very nice find. Congratulations!
See Nocq, v. 4, p. 29.