2026 Update: All available links updated to the Internet Archive where possible:
Back before the Pebble brand was purchased by Fitbit and Google (~2015) a friend gave me a first generation 'Pebble' smartwatch as a present. I loved the simplicity of the e-ink screen and designed a few a square-face version of the Fallout 'Vault-Tec' Industries' watch face for it.
My favorite watchface among those I put together is a revised version of 'Vault-tec 24' by Microbyte: I changed it to look better on a square original Pebble watchface, and to use 12-hour time measurements instead of the grainy/circular 24-hour one it had originally.
Vault-Tec 12 by Blayne: Download
How?: Using image editing software, as well as the Pebble Image Converter to properly dither image resources correctly while not looking too pixelated.
Then upload that .PNG image to the Watchface Generator v2 and add in/control the overall appearance. It lets you choose and adjust just about every conceivable detail.
Afterward, use a QR code reader App to easily open the URL on the phone which is paired to your Pebble watch. I made sure it opened in my default browser, so it could properly hand-off the URL to my Pebble iOS app. From there, as long as there's empty slots in you watch for watch faces, it then automatically transfers the new Watchface to the Pebble by Bluetooth.
Complicated to make, but fun to have.
Original 24h face:

Test shots of various faces on my Pebble + with my original GUESS wide-band leather watchstrap.