Maven Publication - OXYGEN-MARKET/oxygen-market.github.io GitHub Wiki
You can do this on the Bintray homepage.
Once the account is created, navigate to the automatically created maven repository at bintray.com/{{username}}/maven, choose "edit", and tick the "GPG sign uploaded files using Bintray's public/private key pair" box.
(Note: it might be that you instead end up needing to use a keypair generated yourself as described here).
This is documented in their OSSRH Guide.
Further steps are available on the Bintray blog and will be added to this page as they are attempted.