If you look at these ornaments, you will see that they are mostly interlaced ornaments (in Serbian pletenice or prepleti) that are combined with various floral forms. They are very reminiscent of Byzantine ornaments, which is not surprising since the Serbs were initially under the cultural influence of the then powerful Byzantine Empire. It is interesting for Serbian interlaced ornaments (and this can be said for interlaced ornaments of other Slavic Balkan peoples as well) that they do not consist of only one strip, but that several parallel strips (usually 2 or 3) are wattled on them.
You can clearly see that these ornaments are very well drawn, interesting and beautiful, so feel free to use them for various projects of yours whose theme is the Balkans, Balkan Slavic peoples, Byzantium or Orthodoxy.