In final jewelry no. This is why brands like Tiffany are in panic and pivoting to mechanical-watch-like branding, where only inflated price matters.

With close microscopic examination of inclusions and defects, yes you probably can. There are also spectroscopic differences. In general looking at finished jewelry, no, not really.

De Beers sells devices that can distinguish between naturals and CVD synthetics. They're not cheap, but less than ~$80K, IIRC. They do a pretty good job, I've heard >90% success in identifying CVD stones.

There are some applications, such as IR optics, where natural diamonds aren't pure enough.

DeBeers has been working on systems to do that.