You can set up a signature for your HubSpot user profile, which will be used for your emails sent through the CRM.
In your HubSpot account, click your account name in the top right corner, then click Profile & Preferences.
Scroll down to the Signature section and click Edit signature.
Enter your signature in the text box. In the Simple editor, use the icons to format the text, insert a link, or insert an image. Or, click HTML and edit the HTML of your signature.
Please note: if you want to customize the font of your signature, you can use the face attribute in a font tag in the HTML editor but be aware that many fonts are not be supported across email clients.