If you've posted your barcode somewhere on a website then there's no way to tell. If you haven't done that then you should know the answer, because you would then need to let the person scan yourself.
If it was on a site you would know I guess too though. Once it's successfully scanned by someone it will request to add you as a contact. So if you've had a lot of requests then your barcode has been scanned that many times.
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