Employees have two fields that indicate their start dates: one for the day they initially joined the company (Original start date) and another for the day they were rehired (Start date). In cases where an employee has never been terminated, these dates will be identical.
You can use this information to set up a formula that highlights whether an employee was rehired or not. Here's an example:
Once you apply the formula, locate its name on the column picker and add it as a column. It should say "Rehire" for the employees that have a different "Original start date" and "Start date".