Two men escaped with a cash box after threatening G4S staff with weapons inside Santander, West Princes Street, Helensburgh, at 00:35 on Wednesday.
Police believe a dark-coloured Hi-lux 4x4 vehicle was used in the getaway.
They said a blue high-powered Audi estate and a Vauxhall Zafira may also have been used by the suspects.
The men escaped with a five-figure sum of money.
During a similar early-morning raid at the same branch on 6 April, two men escaped with another five-figure sum of cash.
Police have said the robberies may be linked.
The suspects in the latest incident have been described as being of medium height, medium build and were wearing overalls and masks.
Det Insp Douglas Wilson, from Police Scotland, said: "We continue to seek information on a dark-coloured Hi-lux 4x4 vehicle, which we understand was initially used in their getaway.
"We also continue to seek information on a blue high-powered Audi estate vehicle and also a Vauxhall Zafira vehicle which may have also been used by the suspects."
Det Insp Wilson added: "From the CCTV that was analysed, we observed passengers getting into the back of two silver private-hire taxi vehicles at around 0035 hours.
"It is possible that the taxis may have encountered the 4x4 vehicle making off from the scene at speed. If the drivers or the passengers of those vehicles have any information they believe may be useful to our inquiry - please get in contact."
Three vehicles could have been used in a robbery involving two security guards carrying out cash transfers at a bank in Argyll, police have revealed.