A spate of arson attacks caused thousands of pounds worth of damage in Accrington last week.
In one of the attacks burning paper was pushed through a letter box.
Detectives are appealing for information following the blazes.
The flurry of fires began shortly after 3am on Sunday April 18, when a Subaru Impreza was set on fire on East Crescent.
A second fire was reported a short time later after burning paper was pushed through the letter box of a nearby address on West Crescent.
The following day police received several reports of ‘For Sale’ signs having been set alight the same night on Burnley Road and Queens Road.
Police are linking the incidents and are urging anyone with information to come forward.
DS Paul Langley from Accrington CID said: "We believe these fires were started by the same person or group of people and appeal to anyone with information to come forward.
"I am particularly concerned about the burning paper which was pushed through the letter box.
"This could have resulted in serious or fatal consequences had the householders not had smoke detectors fitted."
Anyone with information can contact police on 0845 1 25 35 45 or Crimestoppers anonymously on 0800 555 111.