What do the numbers and letters on an old porsche mean?

For example 98 on the side of car and AP on the door. I'm pretty sure the car is a 1955 Porsche Spyder 550.|||Without a picture to reference, it's hard to tell exactly what you're referring to.





But... from the factory, the only lettering of any kind that adorned the sides of any of the 550 models was the script "Spyder." This was located on the front fenders just for of the doors.





So whatever other numbers and letters you are seeing would have been added by the owner of the car. The most likely explanation from the vague description you give, would be that the car runs or has run in some competition as number 98 in class AP: while a 550 would not fit into the current SCCA class A Prepared, it may have when it was new or fit in a similar class for some other organization.





As an continuation of that, as just about all 550 models that Porsche sold were raced when new, it's also possible that the car is maintained as it was when it had it's greatest track success even though it's long since retired, or copying the livery of a successful or famous 550 (although #98 is not especially notable to my knowledge, numbers 55 and 130 tend to be the most iconic for this model).