In order to comply with mobile formatting, text-wrapped images can only be bound to the top-right or top-left corners of a text block, so inserting an images into the middle of text isn't possible.
You could potentially setup separate blocks in a single row (i.e. have the signature image text-wrapped to the top-right of your Sincerely text block, then a second text block for Manager, but even that would require a lot of manipulation of text size, alignment, and other elements that may not ultimately look that well crafted. For example:
The best setup, and what I've seen other companies outside of our services regularly use for their emails, would be would be to have separate, single-block rows on top of each other, or example:
One thing to keep in mind is that if your signature image is only as big as just itself without any whitespace to the right side, it will be auto-centered in mobile formatting when opened on mobile devices, which is email apps' default functionality:
To avoid this, I'd recommend inserting your signature, taking a screencap of it with all the whitespace to the right of it, then inserting that screencap instead. That way when it converts to mobile view, the image will still be left-aligned:
See also:
Inserting signature images into emails
... View more