Blue tape has been placed on buildings in the centre of King's Lynn.
The markings, which appeared overnight, are believed to be linked to a climate change protest due to be held in the town later today.
The tape has been placed around 1m off the ground on the Nip and Growler, Boots, Burtons, Goldings, Archers and Lynn Minster.
Today Charlie Gardner, from environmental pressure group Extinction Rebellion, said: "Numerous businesses around King's Lynn have joined a climate change-themed art installation by agreeing to have blue tape across their shop fronts.
"The tape marks the level that flood waters will reach with increasing frequency within a few decades, if we don't act urgently to prevent climate breakdown."
It comes as activists say they do not plan to disrupt a mayoral election when they protest at a council meeting.
Extinction Rebellion group has said it will be attending West Norfolk council's AGM and mayor making tonight.
Members are calling on the authority to declare a climate change emergency.
The council said it was aware that the group planned to attend the meeting, but did not know what form the protest would take.
But one activist said in an e-mail: "At this stage we have no plans to disrupt the meeting."
More than 1,000 climate change demonstrators were arrested as 10 days of protest brought central London to a standstill last month.
And there were four arrests when activists disrupted a Norfolk County Council meeting in Norwich in February.
Extinction Rebellion hopes West Norfolk will join the 100 or so local authorities which have so far declared an emergency, which include its neighbour North Norfolk. Some have declared target dates by which they aim to become carbon neutral.
But one West Norfolk council insider said that as the issue was not included on the agenda, it was unlikely that a decision could be made tonight.
Instead the meeting, at King's Lynn Town Hall, has been called to confirm the election of Geoff Hipperson as borough mayor.
Mr Hipperson, who has been councillor for the Airfield ward since 1999, is currently the deputy mayor of West Norfolk.
He has nominated Watlington-based charity West Norfolk Riding for the Disabled and mental health support group West Norfolk MIND as his mayoral charities for the year.
Mr Hipperson is a former cabinet member for the environment on the council.
Dr Gardner said: "As a low-lying coastal borough, west Norfolk is one of the most vulnerable places in the UK to climate change, and in particular sea level rise.
"In response, we have recently formed an Extinction Rebellion King's Lynn and West Norfolk group to demand our leaders take urgent action."
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