information
crest

Yamato holds the crest of friendship, which at first does not seem to fit him at all (much like Mimi with her purity/sincerity crest).

However, as the anime would be boring otherwise, of course it mustn't be easy for the digidestined to acquire their crest's strength, leading to the conclusion that everyone has to surpass some kind of "test", before getting his/her new power, that is activating the crest's sign through developing the name-giving attribute. In Matt's case, friendship.

Obviously, at first it appears a hard trial for Yamato to surpass, as he has troubles trusting other people and valueing friendship enough. Anyway, as Jou risks his life in order to save Takeru (dramatically spoken), Yamato is able to understand the worth/meaning/ purpose/etc. of friendship and his crest starts to glow.

Moreover there's also a very strong bond of friendship between Yamato and Gabumon, eminently later in the series. This is shown when Gabumon is still loyally holding on to Yamato and battles his friend Agumon for him when he's pitting against the other digidestined/Tai.

The crest's color is blue and it resembles a yin/yang sign.