Prototypes are simply a sample (proof) of a pin design that is created for pre-production inspection.

In some cases, this design is not approved, making the prototype unique in that it was never produced beyond the point of sample. There could be as little as one sample produced, and in rare cases, to as many as a few hundred of a particular prototype design (depending on how many pins the manufacturer produced before submitting the design for approval).

A prototype may also be a sample of a pin's design that does indeed make it into production. It is possible that no changes were warranted from this initial design and the prototype and production versions may look identical other than the fact that the prototype may or may not have a backstamp present. It is also possible that certain colors and/or design elements may have been altered for the production run.