A police spokesperson said the man approached the female at the bus stop in the Park Avenue area around 3pm on April 22 and made obscene sexual comments.
He is described as being in his late 60s with grey shaven fine hair, grey stubble and is missing a few teeth He was wearing black UGG boots, tracksuit bottoms (tucked into the boots) and was holding a newspaper.
In a separate and unrelated incident an attempt was made to hotwire a blue Yamaha motorcycle parked at the Foyle Valley Railway Centre between 4pm and 5pm on April 23.
Anyone with information about these incidents is asked to contact police on 0845 600 8000 or a member of your local Neighbourhood Team directly – details can be found on the PSNI website.
Alternatively, if someone would prefer to provide information without giving their details, they can contact the independent charity Crimestoppers and speak to them anonymously on 0800 555 111.