When coupling a trailer to a pintle hook, how can the driver tell the latch is correctly locked?

AAMVA CDL Manual, Section 6.4.3, Figure 19, p. 6-10 to 6-11

A pintle hook that looks closed but is not actually locked can separate on the road, since there is no fifth wheel kingpin holding it in place mechanically. Confirming the lock handle sits flush with the latch, plus the lock pin is secured, is the only reliable visual check that the connection will hold.