At least at the companies I've worked at and had offers from, the signing bonus is essentially to make up for the annual bonus you don't get the first year. E.

At least at the companies I've worked at and had offers from, the signing bonus is essentially to make up for the annual bonus you don't get the first year. E.g. in the oil industry, a significant chunk of your compensation is usually a cash bonus. Equity is reserved for C-level. The typical starting salary for a new grad PhD or MS in geoscience at the majors is around $110k/year. That usually comes with ~$15-20k signing bonus, that you have to pay back if you leave within two years. However, you don't get an annual bonus your first year. The bonus is ~15% at that level, so it works out to be the same as if you'd gotten your annual bonus your first year.