The person replaced "Leon Smith Parkway" with "Indian Mound Pkwy" by sticking white paperboard on the sign. The addition was written in blue and red marker and included a black sketch of the hill the mound is on.
By 9:30 a.m., the sign was restored to its normal condition.
Oxford police said the street department removed the sign.
Officers had not decided if they would pursue an investigation or if any law was broken.
The person answering the phone at the street department said the department had no knowledge of the sign and hung up on the reporter.
The modification appeared to be an expression of displeasure with Oxford's recent removal of dirt from a hill near the Oxford Exchange shopping center.
Archeologists say American Indians built a stone mound on top of the hill as long as 1,000 years ago.
In the past, city officials said the dirt was destined as fill for a Sam's Club store under construction nearby.
Officials reversed that statement this week.
They also said the hill would not feature more development, counter to earlier statements.
Mayor Leon Smith also claimed the mound was the result of natural forces, despite an archeological report commissioned by the city that says it is man-made.