Hi Adam - it depends on what your email signature looks like. If you are just using name, job title, etc. you can use tokens which will change automatically with the information in Marketo, but if you want to include the lead owner actual signature, LinkedIn, etc. I would use snippets. With snippets you would just need to create the segementation, and then create a snippet for each lead owner which can be as custom as you would like and they can look differently for each owner - that's what I do. Hope that helps!