Gmail — 6 steps, ~2 minutes

Copy button included below

1
Open Gmail in a browser and click the gear icon in the top right.
2
Click "See all settings."
3
Stay on the General tab and scroll down to the Signature section.
4
Click "Create new," name your signature, then click Create.
5
Click inside the new signature box and paste your signature.
Make your signature first →
6
Scroll to the bottom and click "Save Changes."

Good to know

Gmail counts embedded images toward its 10,000-character signature limit. If you get an error on save, resize your images and try again.
You can set separate defaults for new emails and for replies, further down the same Signature section.
If you keep more than one signature, switch between them per email with the "Insert signature" icon in the compose toolbar.