Stealth Casting

In some situations you may attempt to hide the act of casting spells, cast them in a non-threatening manner, or disguise the use of specific components as part of the spell casting.
  If a spell has a Verbal component, you must roll Intelligence(Stealth) or Wisdom(Stealth) opposed by Passive Perception if you are not actively observed, or Perception Roll if observed. Loud background noise give advantage to the your roll. If the observer knows that you are able to use magic, they have advantage to the Perception Roll.
  If a spell has a Somatic component, you must roll Dexterity(Stealth) opposed by Passive Perception if you are not actively observed, or Perception Roll if observed. Lots of nearby movement (such as a crowd) give advantage to your roll. If the observer knows you are able to use magic, they have advantage to the Perception Roll.
  If a spell has a Material component, you must roll Dexterity(Sleight of Hand) opposed by Passive Perception if you are not actively observed, or Perception Roll if observed. If the observer is trained to recognize spell components, he has advantage to the Perception Roll.
  If a spell has multiple components, you must roll separately for each. Failure to one roll reveals only suspicious activity unless the observer has studied magic. Failure to two or more rolls reveals unmistakable evidence of casting magic.