Please don't go away.
There's a first time for everything Forfarian!
In Glasgow, seamen and their families shopped in "Marine Stores", very much like the old co-operative stores most of us still remember.
The marine stores allowed credit on the condition that the sailor left his official seaman's papers with the store and these couldn't be retrieved unless the slate was wiped clean. This meant that he couldn't go back to work until he'd paid his bill.
So, when times were hard and money scarce, the men used to change their names, apply for new papers under that name and sail off leaving their debt unpaid.
