An update. A week or so back there was a photograph of a notice on the Jomtien Immigration door stating that 90 day reports had to produce their bank books. A friend has just left and says there was no such requirement.
TLDR : Answer Summary
There seems to be conflicting information regarding the requirement to show a bank book for the 90-day report at Jomtien Immigration. A recent notice suggested this was necessary, but a friend who recently visited reported that there was no such requirement.