The problem with coins is that they vary widely in size within any currency, and are very country/trading area specific/limited.
The beauty of a CD--for which I would include DVDs & Blue-rays, is they are universal as much as anything is; have a very standardized size, and more than one point of accurate reference--the outer diameter, the inner diameter, the writing around the centre; the thickness.
From an artistic point of view, the reflective rear surface opens up any number of possibilities.
Hm. This is a silly poll, and yet, we're taking it seriously. It's that coders instinct to want to solve the problem I guess :)
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"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.