For what its worth, I have my Lemania Silverstone in front of me. My hands are like the example shown by Jeff at OTD, my crown is unsigned and there is no serial number between the lugs. I haven't opened the back, so who knows what is on the rotor, but my guess given what I mentioned above is that it will signed "Lemania".

Fabrizio is the expert on the 5100 series- I have owned three myself (AudiSport, 510.501 and the Silverstone) and all of them have/ had the characteristics that Fabrizio mentions.

I certainly agree with Bullitt's point that it was very hard to keep track of what Heuer where up to during that period, and while its not possible to rule out some inconsistencies in the production (some with signed rotors, some without), it is 100% clear that the majority of the 5100 series were not signed in all of the places that one might normally expect- and so to consider signed components as a definite sign of originality will lead to disappointment...