In the situation you describe, the key issue is that in order for the signed jersey to be translated into monetary value, it would need to be sold and replaced with viable currency. There are several reasons for this.
In the first instance, money must be uniform. While the LeBron James jersey is a uniform of its own, it is not uniform in the sense of matching the accepted form of currency in circulation. It cannot be compared, in terms of worth, to a pair of shoes because the uniform measure of worth is the medium of money or currency, with which we put a value to both shoes and the jersey.
While the jersey is certainly durable, portable, and of limited supply—all characteristics of money—it falls down on the "acceptability" criterion. Humans historically made use of barter systems, but these fail because it is difficult to determine or demonstrate the relative worth of two items without resorting to an intermediary, such as viable currency.