Re: Cotter pins, split rings, or safety wire?
Depending on the type of turnbuckle, you will see different solutions however all of them should do the same job which is preventing the turnbuckle from unscrewing.
The more common methods are cotter pins, split rings, lock nuts (on the RH thread end) and safety wire.
Providing they prevent the turnbuckle from coming loose, can't catch lines (or skin) and don't fall (or break) off, then they are all good.
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence