Download your HTML email signature file and open it in Notepad if running Windows, or TextEdit if you're running macOS.
You should see your email signature's HTML code. Press Ctrl + A (Cmd + A for Mac) to select all, followed by Ctrl + C (Cmd + C for Mac) to copy it.
Login to HubSpot in your web browser and select your username at the top right of your screen. Select Profile & Preferences.
Select the Email tab at the top of the General page, then under the Configure heading, click Edit email signature.
Switch from Simple to HTML at the top right of the window, then click inside the signature field and press Ctrl + V (Cmd + V for Mac) to paste your copied signature code.
You'll notice that you can't save your signature due to a certain tag being in your HTML code, so we need to remove this.
Scroll to the top of your signature code, then find the tag that says <style. Select at the start of the <style tag, then drag your selection down to the end of </style>. Once you've selected from the opening and closing style tag, hit delete.
You can now click Save.
Close out of your preferences and compose a new email. Your email signature will now automatically insert when emailing from HubSpot.