Having a safety system in place at your table is a simple and easy way to keep a good vibe.
 
Whether you're playing with a new group and don't yet know what might make them uncomfortable, or you play with your closest friends so you don't want to unintentionally make them uncomfortable - a traffic light system is just an easy way for players to signal to the game master they are all good even if the character is distressed (green), that they want to address something making you uneasy or they need a minute (orange), or that they can't continue with the roleplay or story - a full pause (red). 
 
With a group pack, each player can have their own set of cards they just keep with their notebook, to raise for the DM's notice if they need. Or with a single set, you can lay them on the table during games, with players knowing they can grab one if needed. As a safety tool, they're something that may not be used often - but that's what safety tools are for, if a time comes up when they'd be needed then they're already there.
 
TTRPG's are best when everyone at the table is having a great time. 
 
Item Specs:
Single pack - One pack of 3 colour system cards.
Group pack - 5x packs of 3 colour system cards.