From BR Bullpen
Once selected in the amateur draft, players are offered signing bonuses as inducements to sign with the major league franchise and begin their professional careers. These bonuses are often determined by the slot of first round picks or the round of later picks.
Signing bonuses for first round picks typically run in the millions, but may drop off quickly after that to just a few thousand dollars for players in the 40th round. Once signed players are paid the standard minor league salary which is considerably less than the major league minimum salary.
Players who play only baseball, have completed their senior year of college or may not qualify to play college baseball academically typically have little leverage and may be offered a signing bonus less than that of a high school senior or a player with scholarships to player other sports. Players like to sign for less than the average for their slot or round are often called signability picks.