Tourists are being warned to stop putting stickers over a big road sign in Kanchanaburi's Thong Pha Phum district that has become an unofficial “check-in” point for visitors travelling the highway.

Local officials issued the warning on Wednesday, saying the culprits could face legal action.

The sign is on a tall frame above highway 3272 and tells motorists they are approaching Ban Pilok.  

Tourists have attached stickers to the poles and also climbed up to attach more on the Ban Pilok sign itself, officials said. 

After passing the sign motorists must drive 399 curves over the next 63 kilometres of road to visit Ban E-Tong, where there is a popular old mine.

The local highway office will put up signs prohibiting attaching stickers and climbing up to the sign.

Officials said the tourists are damaging government property, obscuring the sign and breaking the highway law. Offenders were liable to up to six months in prison and/or a fine of 10,000 baht.