Click Settings → Personal Information → Spatial Information directly in the space to insert a picture into the signature file.

For Baidu, you have to upload the picture to a webpage (such as a space photo album) first, then right-click the picture and properties to get the address (url) inside, then create a group in the signature file, paste the picture address, and then it seems to be ok. Baidu can set up five sets of signature files, and each set of signature files can accommodate several Tu Tu.