When the Gen II RSV was released in '99, the thing that made my breath catch in my throat was the obvious similarity to classic, stately automobiles of the late 1940's and early 1950's in the lines and details of the bike - Studebaker, Nash, DeSoto, and Tucker 48 et al.
I think that with the Stratoliner, Yamaha looked back further, but drank too much pre-WWII art deco hooch and lost the signal a little, though they are very nicely finished motorcycles.
Now with the new SV Eluder and Transcontinental, Yamaha's designers have clearly channelled the 1960's, but in the same modern design language we see in today's modern muscle cars from the Big 3 - Camaro, Challenger and Mustang. I happen to think that they missed an opportunity here, in choosing a V-twin over the V4, the latter echoing much more the character of a souped V8 motor than the former does any automotive engine I can think of.
I happen to love this common thread, having grown up with a greaser gearhead of a father, who build and raced stock cars and street rods in the '60's.
The Italians seem adept at honouring Ferrari and Lamborghini with lovely details on their bikes from time to time, Ducati in particular. Aside from that, can you think of any other motorcycles that really evoke a particular element of car culture?