Volunteers found a pencil caricature hidden on the back of a wooden panel during a project to restore an 1890 carriage to its original splendour.
It showed a man with a high collar, pointed moustache and satisfied smirk.
Bosses at the Midland Railway Trust in Butterley, Derbyshire, speculated a builder decided to tease the management.
The coach was found in 1999, being used as a changing room for a tennis court.
Despite it being a third class coach, restoration involved relatively luxurious fittings.
Velvet seats, gas lights and mahogany panelling had to be repaired or replaced.
It was during this work the doodle was found.
Alan Calladine, the trust's development officer, said: "You often see these doodles and calculations on the back of boards, but this one was obviously something of a caricature.
"It is fascinating to see something which has such connections to the people that built these carriages.
"It is a gentleman in a posh frock coat, with the collar and the rest of it, and a rather striking moustache - so we are assuming it may have been one of the people in charge of the carriage works at that time.
"Perhaps it was the boss that had been walking around and the man working on the carriage did a quick caricature as he went past."
The drawing has now been hidden once more. The carriage will be unveiled to the public during the May Day Bank Holiday.
A 19th century "joke" possibly aimed at a Victorian boss has been uncovered during work at a railway museum.