From 1971 until 1995, all watches made in Switzerland with gold applied markers or gold dial plates were required to have the ‘APRIOR’ logo (often called ‘sigma,’ after the Greek letter) marked on the dial. APRIOR stands for Association pour la Promotion Industrielle de l’Or.
With Patek Philippe watches from this period, the APRIOR mark can be seen on either side of the ‘SWISS’ under the 6 o’clock baton. For many watches, only the batons or numerals were made from gold but this still earns them the right to display the APRIOR logo. Watches made with gold plates would also have the APRIOR.
These marks can be very useful in determining if the watch has a service dial – a dial that has been swapped during routine servicing – but you need to think logically based on production dates. For example, I recently saw a ref. 1450 made and sold in 1953 with an APRIOR dial. Without a doubt it had a service dial since the watch is from 1953 and the dial was from after 1971. Conversely, you may also come across a watch made in late 1998 with an APRIOR dial. In this case it is highly unlikely that an APRIOR dial is original on a watch produced three years after the APRIOR era ended.
For collectors, these details make all the difference.
