The police later arrested a man in connection with the incident.Pictures on Twitter showed that the man was wearing a burka.
Notices are available for inspection normally in the Customer Service Centre, at the Town Hall.
Office hours are am to pm, Monday to Thursday and to Friday.
They are appealing for information to find a female dog walker who they believe may have important information about the incident.
A statement on the constabulary’s Facebook page said: "The woman was walking through Watford Town Centre around the time of the incident and may have seen the suspicious device prior to it being reported to the police."Earlier today, police asked people to avoid Watford Town Centre after the item was found in Market Street at 11am. Market Street, the High Street and the Ring Road were closed off while a disposal team destroyed the device.“An Explosive Ordnance Disposal team is currently in #Watford town centre assessing the situation,” tweeted the police.
The Evening Standard reported that the man was carrying two rucksacks filled with children's books.