Ligatures for “ль” and “нь” are unique to the Cyrillic alphabets of several Slavic languages in Southeastern Europe. We don’t have them in Bulgarian, so I can remember being confused the first time I saw them in Serbia. My confusion turned into fascination once I realized that their construction fused two characters that I knew how to use into one that we simply don’t have.
You can see љ (Lje) on this road sign for Жељуша in Serbia (with the Serbo-Croatian Latin representation below it):
