Who's the target market for this? Most marketing teams want analytics on the actual links in the email body, rather than the signature. And if they had that in place, then tracking the signature is pretty simple addon.
It's also great for charities, schools and political campaigns to raise money.
For charities, yes I see the value, although I'm not sure if that is a huge revenue source.
Broad 'newsletter' emails don't get read as much, because they're not going to contain specific relevant information to customers' existing orders or other information they need.
In contrast, a service like this allows a little promotional banner to be shown to customers who are almost certainly going to be reading the email, because they are placing an order, checking up on an order, or inquiring about a product. And below the email from the salesperson/CSR, you can promote a relevant product or message that is highly likely to get read. The traditional way has been to badger salespeople until they change their signature, which doesn't work very well. Now, it's all automatic.
To the founders: there are a lot of people on here who seem not to understand your product. That's OK, I don't think they're in your target market and don't appear to have the painpoint you're solving. In most of traditional corporate America, this is a big pain point you're solving, especially for the poor marketing people who are tired of trying to get those signatures updated.