Money has been stolen from a backpack belonging to a man in his 70s.
Residents and visitors in the city are being urged to "stay vigilant" following the theft, which took place on St Peter's Street between 11.50am and midday on Wednesday, March 16.
Hertfordshire Police has issued advice to help residents and visitors keep their belongings safe.
Sergeant Mark Williams, from the St Albans Safer Neighbourhood Team, said: "I would like to urge residents to stay vigilant as there have been other similar reports in the area.
"Remember to keep purses and bags closed and secure at all times.
"It is also a good idea to carry bags in front of you or diagonally across your chest.
"Make sure to use a purse that’s difficult to open.
"One that zips or snaps shut is best, and keep it closed.
"If you suspect that pickpockets are in the area, report your concerns by calling 999."
Hertfordshire Police has also released CCTV images of people who might know about the incident.
Sergeant Williams said: "We believe those pictured were in the area at the time of the incident and we are keen to speak to them because they could have important information.
"If you recognise them, or have information yourself, please get in touch."
Anybody with information can file a report online (https://www.herts.police.uk/), or contact the force on 101, quoting crime reference 41/21154/22.
Alternatively, anonymous reports can be submitted to CrimeStoppers on 0800 555 111 or online: https://crimestoppers-uk.org/
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