Even if they belong to different Guild Alliances, they can still sense each other, because the Guild Alliance's main contract can sense contracts from other Guild Alliances.
Unless the person is unaffiliated with any guild, in such cases, the people from the Guild Alliance wouldn't be able to detect them, and they might be mistaken for Ocean Town residents.
Of course, it's not entirely impossible to differentiate, for example, using detection ability to probe the other party's information would work.
However, if the other party carries a Concealed Origin Stone, then it's impossible to investigate.
But generally speaking, the Ocean Town residents won't carry a Concealed Origin Stone, which feels a bit like trying to hide something that everyone knows.
Although I can't sense which Guild Alliance you belong to, if you're carrying a Concealed Origin Stone, then you're most likely unaffiliated with any guild, and such people are often spies sent by certain Guild Alliances.
