The PHB and basic rules describe Sleight of Hand checks as follows:
Whenever you attempt an act of legerdemain or manual trickery, such as planting something on someone else or concealing an object on your person, make a Dexterity (Sleight of Hand) check. The DM might also call for a Dexterity (Sleight of Hand) check to determine whether you can lift a coin purse off another person or slip something out of another person's pocket.
Say Bob wants to steal Alice's wallet without her noticing. As a DM, should I call for only a Sleight of Hand check, or also for a Stealth check, to determine whether Bob manages to do it without being noticed?
While the description doesn't mention anything about being furtive while stealing these things, planting implies it is without the person's knowledge. But then again, Perception checks are (always?) pitted against Stealth checks to determine whether someone perceives something else.