Two electrons occupying the same orbital are distinguished by:

According to Pauli's Exclusion Principle, no two electrons in an atom can have the same set of four quantum numbers. If two electrons occupy the same orbital, they have the same $n,l,$ and $m_l$. Therefore, they must have different spin quantum numbers ($s$), i.e., $+\frac{1}{2}$ and $-\frac{1}{2}$.