You can have token-based signatures in Sales Insight emails, but it's limited to the record Owner's info, which was really quite a surprise. Ideally, there should be a token for the logged-in user's information.
So you have two choices, use snippets and have a signature for each sales rep or have the default signature be that of the record owner with the option for the rep to change it manually if the sender is not the owner. The first works fine with segmentation, but isn't really scalable. The second is also less than ideal.
Time to post a new Idea 🙂