What about asking masked individuals to uncover momentarily (long enough for a security cam to record the face) and then cover up before entering your staff members' 6-foot zone?
A robber won't want to comply. But some customer's might not be happy, either, since that compromises whatever minimal protection the mask provides.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8