Mystery Latitude/ Longitude slate

I beautiful sunny, bright day if a bit crispy. Another dusting of snow overnight and today’s walk was along the Centenary Walk in Bridge of Allan. It was bracing andrutted and icy underfoot. When I reached the Hallow’s Lynn I noticed a slate with latitude and longitude on it attached to a shrub growing there. Don’t know why it’s there and who put it there. It’s a mystery?