At the moment, the Pandora application on Samsung Blu-Ray does not have a sign out feature, so we have to manually remove the account association from the device on our end. We are working with Samsung on releasing an update to the application which will hopefully include a sign out feature.
Please email us the email address of the account that's currently signed in, as well as the device's MAC address. This address is displayed in the first line here:
Setup -» Network -» Network Connection Test
(In some versions this is Setup -» Network Setup -» MAC Address)