The signs went up on Wednesday as the first step towards the new multi-million pound cinema and restaurant complex on St Catherine's Road.
Archeologists move on to the St Catherine's Road car park site on Monday to start exploratory excavations. It means that the car park to the rear of the Tollemache Inn will be closed to allow trenching and investigation.
Councillor Jacky Smith, Cabinet Member with responsibility for major development projects, pictured with the Leader of the Council, Councillor Matthew Lee, said: "I'm delighted that activity is about to begin on the site. Our area is steeped in history, so this first step is very much looking to the past by investigating the archaeology of the site.
"We can then begin looking towards the future and a fantastic new, and long awaited, facility for Grantham and the surrounding area."
Owners and cinema developers SKDC expect the car park, which is used by the public on evenings and weekends, to remain closed for up to three weeks.