I agree with HotButton, fancy signatures appeal to people, but they don’t realize how problematic they are. There are dozens of different email clients and nearly all have their own settings options, which guarantees that no matter what you do, some people won’t see what you want them to see. Images will be missing and the text will be styled differently.
Anyway, if you’re doing this for someone who’s dead set on it in Gmail, one trick is to build the signature in HTML/CSS, display it in a browser, then cut and paste directly from the browser into Gmail. There might be ways around it (not sure), but I’ve never been able to write HTML directly into Gmail and have always resorted to the copy-from-a-browser method.
For example, the following code displayed in a browser and pasted into the online Gmail composition window looks like the screen capture I’ve pasted in. Adding the logo beneath is the easy part, so I didn’t bother. Like I mentioned, though, whether the recipient sees it or not, is another matter. For additional backwards compatibility with older email clients, you could do the same thing using HTML tables instead of CSS.
<div style="border-left:5px solid #04c; padding-left:10px; font-family:sans-serif; line-height:1.3em;">
<span style="font-weight:bold; font-size: 1.1em;">Employee Name</span><br />
<span style="font-size: 1em;">Employee Title</span><br />
<span style="font-size: 0.85em;"><a href="mailto:firstname.lastname@example.org" style="text-decoration:none;">Employee Email</a></span><br />
<span style="font-size: 0.85em;"><a href="https://company.xyz" style="text-decoration:none;">Company Website</a></span><br />