What mechanisms exist in AWS to identify responsibility and ownership of workloads?

If your concern is more on what AWS takes responsibility and ownership for, then you may refer to https://aws.amazon.com/compliance/shared-responsibility-model/

However, I believe this question on Operational Excellence focuses more on the workloads and services you run in the cloud. Therefore for each workload or scenario being run in the cloud, there has to be someone/ a team that will take care of that workload.

For instance, all s3 buckets, as much as possible should be tagged according to their owner. In that manner, anyone would know who is responsible for each bucket.

I hope you find the link below useful:

https://docs.aws.amazon.com/wellarchitected/latest/operational-excellence-pillar/ops_ops_model_def_resource_owners.html