Hey! It's actually a cinch to fix the signature editor although it's not immediately obvious (that's why my Switch code is above the Avatar--I couldn't figure it out for a while either lol). If you scroll down beneath the textbox for editing signature, it asks you for:

SIGNATURE PICTURE
Upload Signature Picture
Option 1: Enter the URL to an Image on Another Website and here it automatically has https://www filled in. You have to backspace that out because it processes as a broken URL and will deny you the edits. When you backspace it out, it allows you to save your changes.