Are half-elves immediately obvious to other elves?

I'm wondering if in the Lord of the Rings (and others of J. R. R. Tolkien's works) the differences between elves and half-elves were clear enough that an elf meeting an half-elf would be immediately aware of their origins, and vice-versa. From what I understand, half-elves looked pretty much like regular elves, but perhaps elves have some sort of sixth-sense in this matter?