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if you put your Bless in a bankbox or secure container
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Actually, you're only half right. UO's code sees the bankbox as part of a character's inventory. This is why UOE in the early days had it's "bank anywhere" feature.
For this reason, when dropping a Siege blessed item in the bank, it will not unbless. Locked down containers, secure containers, the floor, etc...it will unbless.
Also, you cannot trade blessed items, I believe...