Due to the way these changes are communicated to the Maximo system (via REST API) I don't think e-signature is supported yet. The REST API in recent versions (I believe 126.96.36.199) added supported for e-sig but it requires adding additional query parameters to check if an e-sig enabled attribute is modified and then a UI would have to be built for the user to provide their credentials (or e-signature key, if using the new 188.8.131.52 functionality) again.
The new UI framework used by Maximo Mobile (sometimes referred to as Graphite, which is based on IBM's Carbon Design) does have e-signature support on the backlog so I know it's planned to add there. I've not seen anything about this regarding Work Centers. I would open an Idea (formerly RFE) if this functionality is important to you. You can do that here: https://ibm-ai-apps.ideas.ibm.com/ideas/