Turn Signal Cadence

Are there legal requirements for turn signal cadences?  Does it have to be on-off on-off ?

I’ve seen the mustang tail lights that go “>00”, “>>0”, “>>>”, repeat and I happen to like that.  Was thinking you might differentiate with a PWM-like fading for your signal vs toggled on/off.  Or maybe more Morse-code-esque?  short short long … long long short .. something like that?

…random thoughts…