The repro's are made from the original molds - so the shape is exactly the same.
Look for obvious wear on the bottom of the base: dirt, paint spatter/drips, chips, etc.
Also, new reproductions are 'whiter' than most originals. Most originals are a bit on the 'blue' side - but you'd need to have one of each side-by-side to really see the difference.
Later . . .