A man allegedly exposed himself while sat in a doorway of an empty shop in the Bailgate area of Lincoln.
The incident on Gordon Road in Lincoln was reported to Lincolnshire Police at around 4.27pm on Wednesday, September 11.
Police published an appeal on Tuesday, September 17 saying they believe others may have witnessed the indecent exposure.
Any witnesses or anyone with information to assist the investigation should contact police on 101 or via email at [email protected] quoting reference 278 of September 11.
It can also be reported through the independent charity Crimestoppers anonymously on 0800 555 111 or online here.