You are using the Outlook agent: Following the creation of your signature template and its deployment, when you start a new e-mail, your signature seems to have dotted borders applied to the template, even if you have not defined any borders in the signature design.
Please note that once your e-mail is sent to your recipient, no border/grid appears on your signature.
There is a solution to this problem:
Open your Outlook mailbox.
Generate a new email and make sure your signature template is applied.
Click inside the body of the email, select the Format Text tab (in the top ribbon bar).
Click on the Borders drop-down menu
Click on Show Grid to deselect this option