What is that big neon sign beside Glasgow's M8?

Above the busiest stretch of road in Scotland, a giant neon sign greets motorists with a bold and puzzling message.
It says: "IT IS GREEN THINKS NATURE EVEN IN THE DARK".
For the past few years the 3m red letters have illuminated Glasgow's skyline.
By now, millions of motorists will have ed the sign at junction 21 of the M8 and undoubtedly thought, "What does that even mean":[]}