Click these links for an image posted at ABPR / Railfan.net:

Railfan.net ABPR Photo-Mopac HERB-1 - boxcar, Dolton, Ill, March 26,1981 - Thomas Goldin Photo/Peter J. Vincent Collection

Railfan.net ABPR Photo-UP HERB-1 - Looks the same, but different. A later version on another car with UP shield, 1987.- Glen Beans Photo

Railroad.union.rpi.edu Photo "Herbie" Graffiti - closeup of graffiti on Atlanta & St. Andrews Bay box car no. 8082 found in the Milwaukee yard in Mason City, IA, on August 4, 1977. - SD Marty Photo

Graffiti History 101: Just Who Was Herbie?
The Herbie drawing began appearing first as graffiti art on freight cars - a large number of these being owned by the Mopac.  The Mopac later adopted the art for use with a safety slogan on a boxcar stationed out of Little Rock.  It is still in use on the Union Pacific R.R. today. 

Herbie Meyer was the original artist behind the fellow enjoying his siesta under a sombrero resting against a palm tree drawings. The name Herbie followed by a date was always under him. Herbie worked as a switchman for a yard and transfer company, other than Missouri Pacific, somewhere in the St Louis area, possibly the TRRA (one story has it that he was a switchman on the Wiggins Division of the TRRA in St Louis).

He died December 9th, 1995, when he was in his eighties. He is now a legend in the graffiti community, as more and more practitioners are researching the history of railroad graffiti by railworkers and hobos, and they are finding his prodigious output of drawings on the railcars had an apparent omnipotent presence in vast railroad network for over three decades.

There was an article in the CB Hist Society magazine Cotton Belt Star about Herbie identifying him as a carman at East St Louis, hence so many 'tagged' MoPac and Cotton belt cars. (gathered from the MOPAC Group)

"A story that appeared in the Brotherhood of Locomotive Engineer's Newspaper back in the early 80's told that Herbie was a Car Inspector that worked in the St Louis, MO area for either the Terminal Railroad Association of St Louis or Alton & Southern, but I cannot remember which one it was for sure now. He retired around 1980.

"Herbie told of many who attempted to copy his artwork, but never getting it correct as the number or style of leaves on the tree were never quite right." (Tuch)

MP East One - which was often paired with HERB-1, had the unique distinction of being the sole MP caboose to wear a large "Turbo" eagle. "November 27, 1982 finds Missouri Pacific's Classroom, a converted Drover's Caboose, at Dolton, Illinois." MP East One was recycled by the railroad as a company promo for railroad safety. - Thomas J. Golden photo, postcard