What does “Kirkin of the Tartan” mean?
I’m Scottish descent and raised Presbyterian, and I had never heard of it:
https://churchmousec.wordpress.com/2010/05/16/the-custom-of-kirking-of-the-tartan/
Kirk is Scottish for church. To Kirk the Tartan is to bless (in the church) all things Scottish, but particularly clan colors/plaid.
(There was a 30 year period in the 1700s, following a Scottish uprising, during which the British government forbade the wearing of tartans. To get around it, the clan members would pin a small swatch of their tartan on the inside of their jacket/clothes. At a given point in the church service the pastor would give a signal, and everyone would reach inside their garment and touch the tartan.)