I found the rules
1- '79-98 911's get an enthusiastic wave
2- '74-78 911's get a wave of sympathy
3- Boxsters get a wave only if they wave first
4- Cayenne owners get a hostile stare or middle finger
5- '99-05 911's - see Boxster
6- Pre '73 911's get a wave and salute
7- 356's- see pre '73
8- 914's get a nod
9- 924, 928,944,968 get eye contact
10- "special" Porsches (anything not covered previously)
Use your best judgement.
http://forums.pelicanparts.com/showthread.php?threadid=231387&highlight=cv+joint