Open Settings: Click the gear icon in the top right corner of Gmail, then click See all settings.
Find Signatures: On the General tab, scroll down to the Signature section.
Create New: Click Create new and give your signature a name (e.g., "Work").
Paste Your Signature: Paste your signature from SimpleSignature (Ctrl+V / Cmd+V) into the editor.
Set Defaults: Under the editor, set your signature for New emails and Replies/forwards.
Save: Scroll to the bottom and click Save Changes.
Yes. You can create several signatures (e.g., "Work", "Personal", "Formal") and choose which one to use as default. You can also switch signatures when composing an email.
Only if you set it to. In Settings → Signature, choose your signature under "For replies/forwards." Leave it blank to exclude signatures from replies.