In the 1990s, I traveled into Tijuana from San Diego County a few times. We usually walked, because of reasons.

For people traveling north into the USA, the border checkpoint included long queues of vehicles and people alike, customs inspections, routine searches of everything, passport checks, and questions by actual Border Patrol officers.

Walking south into Mexico, there was a broad, unsupervised walkway and a one-way turnstile. Large signs read:

  WELCOME

  ¡BIENVENIDOS!

  NO FIREARMS

And that was it! We were in Mexico!