From BR Bullpen
A signability pick is a player who is likely to sign a professional contract quickly and for what is viewed by the team selecting him as a reasonable amount of money given his slot in the amateur draft. Often these players receive a signing bonus less than that received by the same pick the year before or the year after. Also, these players may be viewed as not deserving this slot in the draft based solely on their baseball talents.
Agent Scott Boras has never represented a player viewed as a signability pick.