Sidokar, that's very interesting but where do you find info about the style of a specific composer? Suppose I were to take a lesser-known composer from the Baroque, how would I figure this out?
Qazsedcft, Are you talking about the ornamentation or more generally about the way the composer is writing music ?
I was asking about ornamentation in relation to your post.
OK, I understand your question. There are different indications that can be used. Many composers left written instructions or even theory books. At the time theorists were also composers anyway. That is the case for example for Frescobaldi, Diruta, Purcell, Rameau, Couperin... There are a lot of materials being published on the subject.
Secondly some composers did write in a number of ornaments into their score rather than using signs. In fact in early baroque very few signs were actually used. Musicians would know where to put ornaments, that be vocalists or luth, viola, keyboard players ....
For composers who did not write anything nor have detailed out the ornaments, one has to refer to the usual practice or the specific period in the country. So for example for late renaissance or early baroque one can use the directions given by Diruta, Merulo, or later on by Monteverdi or Frescobaldi.
What is important is to understand how the ornaments fits within the style of the composer, assuming one is interested by the historical style.
But during the classical period, the number of signs started to reduce and get standardized, so the issue becomes quite limited. There are a number of clocks that we have with Haydn music as well which have been used to determine how his ornaments should be played.
Of course you have people who compiled and give summary views usually by period/country. There is plenty of litterature on the subject. Now to be honnest most amateurs play only a few composers. For the baroque, it would be essentially Bach, Scarlatti, Haendel, Rameau may be. Few people will play Froberger, Frescolbaldi, Couperin, Chambonnieres or more exotic composers. So the question gets quite narrowed down.
So I think a few basic rules plus whatever written indications are available (the famous Bach table of ornaments, or Purcell table, Rameau) gives a start base which is good enough for beginners amateurs.