[ AR has not gotten the opportunity to see this postcard and he doubts he will ]
That depends entirely on the interpretation of the situation and the nature of the act itself. Was it committed with an intent to harm? The information could be used for malicious purposes, of course, but if that malicious action hasn't been committed then I doubt that this action in itself would be prohibited. [ Probably. ]
I would not worry about it.
... Yet.
[ AR finally decides to put the bag away in its proper place. The unexpected, he is sure, is the expected by this point. Any would-be thieves will be stumped, AR's sure ]