I have a different perspective on this compared with other commenters... Intelligence is very hard to fake.
What's the best way to signal guitar playing skills? Play the guitar, and play it well!
The efficient way to signal intelligence is: to do worthwhile things, intelligently!
How can you tell if someone is doing things intelligently?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
(I plan to make these threads from now on. Downvote if you disapprove. If I miss one, feel free to do it yourself.)