Symbols are items you can create in the "Designer" screen. The Designer screen can be accessed via an actual Designer terminal, or within the Vehicle or Clothing customization areas while adding a decal to one of your possessions
Symbols can be exchanged with other players as well, on the marketplace or in Email.
Some design controls are only available in the designer, and not available in the decal placement screen under clothing and vehicle customization, such as being able to select multiple layers at once and resize them all at the same time. This is critical for being able to put words or sayings on your items.