The signature of the 50/1.4 is pretty much that it ain't got no signature. It doesn't really do much of anything except produce sharp, contrasty, artifact-free images. In these aspects of performance it's slightly behind an ultra-modern aspheric optic such as the 50/1.5 Nokton, but not by much.
In that regard it is, of all the high-speed 50s from the classic RF era, probably the closest to a modern high-quality Japanese generic 50. It's an unobtrusive optic, the opposite of the kind of self-promoting lens that makes cognoscenti exclaim, "Ah, yes, the unmistakable off-axis highlight flare that distinguishes the 47mm f/2.6 Regno-Bloviatar!"
If you look up
Sean Reid's review on Luminous Landscape of fast lenses for the Epson R-D 1, you can see some examples of what its images look like (on an R-D 1, at least.) As well as the example pictures, Sean contributes some intelligent commentary about the image characteristics of each lens he tested. While he demonstrates conclusively that the 50/1.4 isn't as sharp, especially in the corners, as the modern Voigtlander Nokton or Leica Summilux lenses, I didn't see enough difference in his sample pictures to convince me that I should spend the money (which in the case of the latter is considerable, cough, choke) to replace my Canon with one of them.
