Two 20 amp circuit breakers installed with copper wire bridge
The nail/wire is not a legal handle tie, but a proper electrical supply who deals in that brand will cheerfully sell you one for $3 - or as Ed Beal points out, anyone will sell you a 2-pole breaker for $9.  Whether that is legal: It depends.  

If the breakers are powering device(s) that use both 120V and 240V (classically ovens (for the light) and dryers (for the motor)), then that device requires common-trip.  Handle-ties cannot provide common trip.  Only a 2-pole breaker can do that. 

If the breakers are powering a variety of loads, every single one of which is a 120V-to-neutral load, or every single one is 240V-only (no neutral: water heater, A/C, EV charger), then common trip is not required; you need common maintenance shutoff.  That is what a handle-tie does.  But you need to use the proper one that is UL listed for the breaker type.