The incident took place at Lock 19 near Allandale football field at around 3.50pm on Friday, July 12.
A 44-year-old woman was walking on the Forth and Clyde Canal path when the man exposed himself to her before performing a sexual act on himself and cycling off.
Despite extensive inquiries, officers have been unable to trace the suspect, who is described as white and 5ft8ins with a stocky build.
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He was wearing a dark maroon or brown top, grey shorts and brown walking boots and was riding an older looking red metallic bike which appeared slightly too small for him and carrying a black rucksack.
Officers say the man was also wearing a distinctive silver helmet described by witnesses as being shiny or mirrored in the style of those commonly worn by skateboarders.
Inspector Andrea Campbell, from Falkirk Police Station, said: “While the woman was not injured, this was an unpleasant experience and we are conducting local lines of inquiry to trace and identify the person responsible.
“If you were in the area and saw anything suspicious, then please contact police immediately.
“Likewise, we’d also urge you to get in touch if you have any information that can help us determine the identity of the suspect.”
PC Lauren Gavin, local community officer for the Bonnybridge area, said: “Since the incident occurred, we have carried out extensive enquiries and will continue to do so to ensure that every effort is made to identify the male responsible.
“We have conducted numerous foot and cycle patrols in the area and have visited local businesses and properties in neighbouring towns so they are fully aware of the incident and to glean any intelligence or information they may have.
“Despite these efforts, the male unfortunately remains unidentified at this time and we again ask any person who is a regular user of the canal path or who may have been in or around the area at the time of the offence to bear in mind the distinctive description provided by witnesses, in particular the unusual style of helmet worn by the suspect.
“It is reasonable to suggest that this is not the only time the suspect will have used the canal path and it is highly likely that other persons will have seen this male at some point. Even if it has not been on the date or time in question any sighting may still be equally relevant.
“I understand this may be concerning for the public, however, incidents like these thankfully do not occur often and people should continue to enjoy the use of the canal path as normal but remain vigilant.”
Those with information can contact police via 101 and quote incident number 2850 of July 12.
Alternatively, an anonymous report can be made to the charity Crimestoppers on 0800 555 111.