From your Gmail account, you can choose to automatically and immediately include your signature in every new email you compose.
1️⃣ Access your Gmail settings
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From Gmail, click on your settings, then See all settings.
2️⃣ Access your general settings
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From the General tab in the menu, you will find at the bottom of the page the options regarding your signature.
Check the box: Insert the signature before the quoted text in replies and remove the '--' line that precedes it.
That's it!