We've implemented a few different options.
Third party tools like www.symprex.com are good for granular control, better design and easier management. While you can have multiple campaigns and be really customized, we've seen it most often used to just deploy a standard signature across the organization that is updated monthly/quarterly.
You can also do this in O365 with transport rules as well, but it's a little more complicated as senders don't see the signature in their email and it can keep getting appended through multiple replies. You also really should hand code it in HTML so that it looks consistent.
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