If your name is on the following list you have a genuine right to claim association with Clan Sinclair. In Scotland septs are families that followed another families Chief. The smaller “septs” would then be part of that Chief’s larger family. A sept could also follow another families Chief if two families were linked by marriage. If a family lived and/or worked on the land of a powerful Laird they could be a sept of that Lairds family.  Other family names may be associated with clan Sinclair due to adoptions both formal and informal.