Open Baidu Tieba/

Log in to Baidu account.

Click on the gear-shaped logo, and then click on Tieba Settings

Click on the signature file on the page that pops up, as indicated by the arrow in the picture below.

Click to add a set of signature files

Input the corresponding name and picture link in the dialog box that pops up (the picture link is the signature of Tieba)

Click Save and wait for approval by the administrator