Tilt mechanisms from this era often had a post with a slightly concave top where a small ball rested until knocked off by a tiltable nudge. The ball would fall off the post into the surrounding bowl. There was no electrical tilt to stop the game, just a visible indicator that the game had been tilted. The coin slide would typically lower the post so the ball could roll onto the top of the post and reset the tilt at the start of each game.

For an example see:

http://www.ipdb.org/showpic.pl?id=880&picno=20736

The patent is the first on the list at:

http://funwithpinball.com/resources/patents

/Mark