I have NEVER seen this on a tombstone before. Didn't half make me do a double take! I will assume it was a note to incline the reader towards getting their spiritual house in order before it was too late.
Wild mountain Thyme. I am singing the words to that Folk song in my head - we used to sing it at Folk Club in Wareham, Dorset, SO many years ago now. A link to the Corries singing it is highlighted above.