A mark carries a name and a date, so marking one starts with signing in.
Sign-in is not configured yet. These environment variables are missing on the deployment:
TAKEMARK_SESSION_SECRET
Until they are set, this page cannot start a Google sign-in, and saying so is better than a button that fails.
Takemark asks Google only for your name, email address and picture, and keeps nothing else. Published marks stay readable by anyone, with no account at all.