If it is a text signature, just copy it directly or enter something yourself, just like QQ signature.
If you want to sign, you should post it online first. There are special signature pictures uploaded and published in general forums.
Right-click after uploading the picture. Then click Properties to view the address of the picture. Copy the address of the picture.
Then:
Personal center-personalized signature-and then paste it to the picture address-save.
Note that the pasted picture address is [img]/xxx.jpg[/img].
Note that it must start with [img]+ picture address +[/img].
Img means to insert a picture.