Police Scotland are investigating three reports of indecencies in the Helensburgh area.
The incidents reported have taken place the in last few days – police are linking the incidents and appealing for witnesses.
On each occasion, the man responsible has been carrying out a sex act on himself within a small, dark coloured car.
One incident occurred on Monday (March 31) in Dennistoun Crescent and a further two incidents happened today (Wednesday)in South King Street.
Inspector Claire Miller of Helensburgh Police Office said today: “Whilst these types of incident are not common, they are totally unacceptable and something that we need to stop.
“At this time, there does not appear to be any immediate risk to public safety, however I would appeal to members of the public who live, work or pass through this area and may have information which could assist us, to contact the police as soon as possible.
“We have increased police patrols in the area and officers working on this enquiry are studying CCTV footage in an effort to gather more information on the man responsible. I would like to remind members of the public to contact us if they see anyone acting suspiciously or in an inappropriate manner.”
Anyone with information is asked to contact Police Scotland on 101 or CRIMESTOPPERS can be contacted on 0800 555 111, where anonymity can be maintained.