Step 1:
Open your browser and log in to Fastmail. On the top left next to your email address, click the down arrow and then click Settings from the menu.
Step 2:
From the left menu under Mail, select Identities & Fetch. When you see your identity on the right, click the Edit button next to it.
Step 3:
Type your name into the Name field and paste your email signature into the Signature text box. Once completed, click the Save button at the top left.
Step 4:
Your new email signature is now installed! Test it out by composing a new email to make sure it looks correct.