(Full Disclosure, I am with Opensense)
Hi, just an FYI, but we have an app on HubSpot that is meant for email signature management as described. Here is a link to it:
https://www.hubspot.com/product-updates/opensense-integration
The full signatures work with Sales pro sequences. We have a way to manage banners with marketing emails as well. Feel free to reach out to our team to help get all setup.