Rolex crowns have a symbol below the coronet indicating if it's a TwinLock or TripLock crown.. However, the dots or line on the crowns do not only indicate if it's a TwinLock or TripLock crown... Case (and crown) material used is also indicated: (Pic from a German watch forum). Note also the different sizes of the dots! Now, since year 2000, the DD is yet again availible in RG. There can be confusion with the YG TwinLock crown after year 2000 since the YG crown then also got two dots. To sum it up, the TwinLock crowns come with the following lines / dots: Steel: Line YG: Line. However, after year 2000: Two dots (6-digit ref. numbers) RG: Two dots WG: Two dots Platinum: ONE dot There only seems to be ONE exception; namely the RG crown of the Turn-O-Graph in SS/RG which for some odd reason has a LINE and not two dots like the RG crown of the DD in RG.