How Many Years Has This Been Here?

The ad on the side of this building is for a train trip to St. Louis from Dallas on the Texas and Pacific Railroad (1871-1976).  What is amazing to me is that the Grafiti artists
have not trashed it. I have no idea how long this has been on the side of the building but it has to be at least over 30 years old.  It looks like someone began to add some
grafitti at the lower right but was stopped or maybe he just thought that something that has lasted so long deserves respect.