Hi Ack-Ack,
Thanks for the link, quite an interesting article!
I'd say the biggest plus of the P-38 shape was its small visible fin area - that's really helps becoming "invisible".
What I'd emphasize a bit more than Widewing did is that visual signature is aspect-dependend, and the P-38 has some low signature aspects (viewed from the same altitude, assuming horizontal flight) and some high signature aspects (mostly when both engines/tail booms are silhouetted at the same time).
I'd also add that while the P-38 had a fairly low visual signature for a plane of its size, it was pretty large to begin with :-)
With regard to the identification aspect, I'm with Widewing in considering it as an advantage, especially considering that it also helps section/flight cohesion if you can tell immediately who's one of your buddies and who's not.
Regards,
Henning (HoHun)