To add a signature to your Web Mail e-mails, do the following:
First login to your account via Web Mail.
Once logged in, click on Settings.
Click Web Settings.
Select the e-mail identity you want to modify.
Here you can enter your signature.
Click to Save Identity.
Note: When using the auto append feature, the signature will not appear when you are writing an e-mail, but will append to the e-mail when you send it.