What gives away that your new workplace is cliquey?

When there is both Cisco video conferencing equipment and Skype/Teams-certified devices in the conference rooms because they are managed by two different departments that purchased conference equipment separately.

When the person showing you around starts telling you who to avoid.

Secret Teams chats that only the ingroup is part of, yet often at all-staff meetings they mention their inside jokes from the chat and then go “oh whoops only some people will understand haha”

When people fundamentally change depending on who is in the room.

You walk in on your first day and what do you see there?

Humans

No documented leadership hierarchy or organisation structure when there's more than maybe 10 people working there. If you have to waste your time fighting out who everyone is and you can't do it in a single meeting where everyone can introduce themselves, then the place is too big to not document roles and responsibilities officially. It leads to closed circles of people who hold the necessary historical knowledge to get anything done.

mechanical keyboards instead of membranes

It has half a dozen employees.

CloudCoach for me, but not for thee

"On Friday afternoon people go hang out or do table-tennis."