The Whyalla City Council say they will likely be forced to replace a sign promoting tours of HMAS Whyalla at a cost of $1000-1500 after vandals spray painted words over it.
It's one of three signs that have been defaced with spray-paint around the highway leading out of Whyalla, the other two signs being for Toll and the Hotel Eyre.
Council CEO Chris Cowley said it was extremely disappointing to see people take it upon themselves to vandalise public property.
"Visually we're trying to present our city in the best possible light and this doesn't present our community well," he said.
"All this does is put a cost burden back on to the community to replace them."
Mr Cowley said council would attempt cleaning the signs first but it was highly unlikely the graffiti could be painted over.
"To get a metal sign like that made can cost around $500-800 and then we'll have to remove it and replace it just because of senseless vandalism," he said.
Mr Cowley asked that the community stay vigilant and report any vandalism to the Whyalla Police.
SAPOL Operations Inspector Mark Hubbard said anyone with information that could lead to the identification of vandals was welcome to contact police.
"This is a beautiful place and we want to keep it that way," he said.