What are some signs of a good culture at a startup?

Everybody gets along, and are adaptable

Fostering teamwork & providing proper training

High retention rate of all employees, including underrepresented groups, employees but specifically based on a metric that takes time spent at the company into account.

No one at the top were "buddies" before starting out.

That staff are passionate toward the organization and department mission, good and effective communication, positive and organized atmosphere that encourages and considers input of all staff members.