My method: My mothers side comes from Scotland and England, and thru research I have found association with three clans. The deciding factor was that my family would talk about going in hiding and having to change our names to escape prosecution, yet I heard nothing about the other two clans.

Because of that, I choose to only wear Macgregor tartan. I have one in modern, plan on getting one in ancient, and also plan on getting 1-2 in the "rob roy macgregor".

If you have Scottish in your heritage but are unsure if you come from the highlands, you can use one of the ancestry sites. Most of them will require payment though for non-US records.