The first person at the crime scene can clearly mark all potential evidence which provides an excellent overview of all the evidence prior to numbering it. These will not blow away in windy conditions. Two colors (fluorescent orange and fluorescent yellow) allow the first responder to help differentiate between categories of evidence, such as cartridge casings or different types of shoe patterns at the crime scene. Made of thick rubber-like vinyl that’s durable and easy to clean. Compact size fits easily in a pocket or crime scene kit. There are 20 markers per pack.