I doubt if they will allow the on signatures. Initially they were not even allowed on forum ads whose slots go through auctions
Images are not allowed no matter how they are created (CSS, SVG, or data URI). Occasionally I will make an exception for small logos and such, but you must get pre-approval from me first.
Later on, according to
this, they are allowed but with some restrictions
You can include images, but they must be base64-encoded data: URIs. No <svg> tags; SVG images are allowed, but they must be base64-encoded in data
There must be a reason.