INSTALL ON GMAIL (Desktop Version)
Once signature loads, choose EDIT > SELECT ALL
(or press ctrl+a).
Copy the signature by choosing EDIT > COPY
(or press ctrl+c)
In Gmail, click the GEAR icon on the top Right of your inbox and choose SETTINGS.
On the GENERAL TAB, scroll down to SIGNATURE, and PASTE new signature into text box (you will need to highlight and delete anything that's already inside this box before pasting the new signature.
EDIT > PASTE
(or press ctrl+v)
INSTALL ON GMAIL MOBILE APP (Smartphone Version)
If using Gmail's official app to send mail on your device, the app will automatically append your FULL Desktop/Web signature to the outgoing email. (This usually takes at least 4 hours from the time you install it on desktop Gmail).
It WON'T SHOW UP while you're composing the email, but it gets added as it passes through Google's servers.