This is a promising idea. Ideally, legal restrictions such as the minimum wage are supposed to increase the probability that our goods and services are produced ethically. But clearly that is not sufficient.
The challenge is in the implementation. Many 'best places to work for"-type rankings that currently exist are easily gameable; companies have targeted campaigns to e.g. fill out enough surveys to make the list. This makes it very difficult for smaller or less resourced firms to compete.
In order for such a badge to have meaning, the organization or group issuing the badge would need to be able to do the following: a) trace fragmented supply chains to verify working conditions even for “down-chain” workers; b) be accessible to companies that may not have the money to lobby for prizes or put together campaigns; c) have some claim to objectivity.
Perhaps those would be some of the challenges prize participants would take on.