Is hiccups a sign of pregnancy?

No. Hiccups are not specifically a sign of pregnancy. The actual cause of hiccups is not known, but one theory includes stimulation or irritation of the phrenic nerve. Even early pregnancy causes changes in the body's fluid and electrolyte balances which could affect the phrenic nerve directly (or indirectly) - these normal changes could potentially cause hiccups in some pregnant women.
Not usually. Not usually a sign of early pregnancy, some women develop them in the late first or early second trimester, possibly related to changes in the mother's respiratory rate. If you think you might be pregnant, a home pregnancy test will provide a quick and accurate answer to that question, better than hiccups.