I wonder what experience teachers all around the world have made with this method of Kodaly of which I would hold my hand in the fire that it is most successful that I propose to add a new tag: hand-signs
We don't create tags unless we find there is a need for them. Typically this means there are enough questions appearing about that specific topic that aren't already covered by relevant tags.
So far we have had no questions about hand signes, and so few on solfege that these would easily be asked under that tag.
Remember tags are just an extra help to the search engine. It already searches in the body and title of questions and their answers.
I don't believe that such a tag would be super helpful. There already exists a tag 'solfege', which should cover all the questions that would require a specific hand-signs tag.