Hi Tony.

Check this page: http://shostatsky.narod.ru/permon/tv-vga/scardpin.html or http://kevlar.20m.com/scart.html

They seem to be quite good (even though the filename of the first one is misspelled).
They state that pin 8 is dedicated for this differentiation

0-2V: TV mode

5-8V: Video mode, wide screen

9.5V-12V: Video mode

There doesn't seem to be a true differentiation between 16:9 and 16:9 anamorphic though. To differentiate those, the TV set seems to actually look at the video signal.

My DVD player puts pin 8 to 12V(actually 11V) for 4:3 and 16:9 non-anamorphic videos and to 6V (actually 7V) for anamorphic 16:9, which works perfectly for my TV set. Other DVD players might set pin 8 to 6V for non-anamorphic wide screen sources as well though, there is certainly some gap in the definition of the interface.

cu,
sven