There is no regulation that states that dormant account signature cards should be segregated. It is simply an industry best practice to protect the dormant cards.
A few thoughts for consideration...
Technology, particularily imaging technology, has introduced a number of new risks that many banks have not addressed.
Scanning dormant signature cards presents a couple of issues. First, you need to address how you will limit access to the dormant cards (images) to those few that need it. Even if the physical sig card is protected, those with access to the image may be able to copy the signature and transfer it to a check. Second, make sure you have adequate controls in place to prevent someone from modifying the physical sig card and scanning the altered card into the imaging system. Third, make sure access to the actual images is restricted to prevent someone from altering the image.
You will also have to address those accounts that move from active to dormant status after everything is imaged. A process should be in place to segregate the physical sig card and move the imaged card to a restrictive status.
Another issue that we're trying to deal with is imaged or electronic reports. In the "old days," the dormant account list was protected. In many image systems, everyone (or many more people) in the bank now has access to the electronic reports. Access should be limited to electronic reports just like physical reports.
One last comment...I've seen at times banks limit access to the dormant account reports but not the inactive accounts. At these same banks, transactions on dormant accounts reject for a second review, but not transactions on inactive. If I was interested in defrauding the bank, I would start with inactive accounts just prior to them going dormant. That way a second review would not be triggered. It might make sense to eliminate the inactive account designation altogether or at least protect the inactive reports as well. That said, with the proliferation of technology into every aspect of banking, it is getting harder and harder to hide information. It is easy to lock up a piece of paper, but it is not quite so simple to protect data stored on many different systems in many different formats. Job security I guess...
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My opinions are just that...my opinions.