I know. I hope it can help you, and more importantly, it can help more people who are similarly trapped. Please follow my instructions,

First open the space: find the space settings: the space settings include/reply settings/blacklist management/personal center layout/authorization management/dynamic publishing/etc. Find /Space Information/ and click to enter. After clicking in, it will be displayed:

Space name:

Space description:

Signature file:

If/

Space name:

Space description:

Signature file: The content is all empty, but there is still a spam advertisement image displayed at the top.

Now you just need to write something of your own below in the signature file.

Cover up the junk advertising image, and then click {Save} at the bottom after writing it.

After modification, swipe the space under the swipe to display your signature file, as shown in the picture: For example: 111.jpg

Then you can directly write something of your own in the signature file: below.

Cover up the junk advertising image and click {Save} at the bottom after writing it.